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The petrography of the rocks of Hong Kong Jones, William Alfred 1927

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THE PETROGRAPHY OP THE ROCKS OP HONG KONG William Alfred Jones A Thesis submitted for the Degree of Master of Applied Science in the Department of Geology The University of British Columbia April, 19 27 U.B.C. LIBRARY R fl CAT.HO; ; L£* «7 . IIIJAI J tP^ ;• ."*7fl7-ACC. MO. ^ f 6"<?/3*" THB PETROGRAPHY 0* THK ROCKS OF HONG KONG By ?/illiam Alfred Jones A Thesis submitted for the Degree of Master of Applied Science in the Department of Geology The University of British Columbia April, 1927 - TABLE OP CONTENTS -I INTRODUCTION Purpose Acknowledgements Bibliography I II III CHAPTER I GEOGRAPHY General Geography Local Geography 1 2 CHAPTER II GEOLOGY General Geology Local Geology 4 6 CHAPTER III PETROGRAPHY Summary of Igneous Geology Tolo Channel Series Distribution Description Age Volcanio Sediments Distribution Description Age Tai Mo Shan Porphyry Distribution Description Age Hong Hong Granite Distribution Description Age Lan Tau Porphyry Distribution of Hong Kong 12 15 15 15 21 23 23 23 26 27 27 27 36 37 37 38 43 46 46 D e s c r i p t i o n 46-51 Age 52 CHAFFER IV SUMMARY AND C ONCLUSIOHS 53 ILLUSTRATIONS Plates 1-10 I —IHTRODUCTIOIT-Purpose The suite of rocks described in this paper were Bitppliea by the Department of Geology of the University of British Columbia &n& were collected by Dr. Sohofield and Dr. Uglow while engaged on a Geological Survey of Hong Kong and the Leased Territories. This survey is being made for the Hong Kong Government by Dr. R« W. Brock with the assist-ance of members of the staff of the Geological Department of the University. Dr. Brock made the preliminary arrange-ments including a reconnaissance of the area to be covered. He was followed by Dr. Schofield who spent a field season of about six months on the general geology and areal mapp-ing. Dr. Williams spent the 19H5 session studying the sedi-mentary rocks of the area and Dr. Uglow inveetigs ted the igneous geology in 1926. Dr. Brock is at preeent in the fie: ThiB paper is a description of the rocks mapped by Dr. Uglow, based on a Ftudy of the thin Fections end speci-mens of his collection. The writer has been handicapped by not having seen the Ftructiral rel&tions of the rocks in the field and by the fact that the ;^ork of Dr. Broek will modify some of the conclusions at present held regarding the age relations of the different intrusions. The general II geography and geology of Aeia hap been quoted from the works of previous writer** in order to give the reader a better conception of the problems of the Hong Kong petro-graphic province. Acknowledgements The explanation of the work being carried on in China is Dr. Brock*s and is taken from Mr. IT. P. G. Davie' thesis "The Petrography of the Hocks of Hong Kong." This paper was prepared under the supervision of Dr. S. J. Schofield* Dr* ?. C. Phemister has been of great sepistance in the microscopic study of the specimens. Eis keen interest and many helpful suggestions are greatly appreciated. Hhe geology of the Hong Kong area is taken from a preliminary paper by Dr* Brock and Dr. J'chofield. ?he geography of the area ie ouoted from Mr. H# F. G. Davis' paper "The Petro-graphy of the Hocks of Fong Kong." ?^he general geology of Asia is quoted from Dr, Schofieid's "Summary of the Geology of the Grown Colony of Hong Kong." Ill —BIBLIOGRAPHY— 1'he fol lowing re ferencep were consulted : Bancrof t , J . Austen Becker, G» P . Clapp. Char les H. Co*, Arthur Hubert Fea rns ides , William George Fanner, Clarence N. Harker, Alfred "Geology of Coast and IslandB between the s t r a i t s of Georgia and Queen Cha r lo t t e Sound B.C. Geological Survey of Canad8, Memoir 83 , 1913. "Cretaceous Iletamorphio Hocks of C a l i f o r n i a , " American Jour-n a l of Science (3) 31 ,348-357, 1886. "Geology of the Nanaino Map Area" Geological Burvay of Canada, Memoir 5 1 , 1914. "The Geology of the Cader I d s i s Range Merioneth ." Quar te r ly Jou rns l of the Geolo g i e a l Society of London, Volume 8 1 , 1925. "On the Geology of the Arenig Fawr and Moel L ly fnan t . " Quar te r ly Journal of the Geolc g i c a l Society of London, Volume 6 1 , 1905. "fhe Katmai Magma t i c Province ' Journal of Geology, Volume 34 No. 7 , Par t 8, October -November, 1926. "Natural H i r to ry of Igneous Rocks", llacMillan Company, Ne\ York, 1909. "Petrography for Students" Cambridge Geological S e r i e s , F i f th E d i t i o n , 1919. '"Therraometaraorphism in Igneou Rocks", Geological Society of America, B u l l e t i n 3 , 16-22, IPs' IV Holmes, Arthur Idd ings , Joseph P Johsnnsen, Alber t T,indgrent Walderaar Moore, K» S. Parsons, A. L. "Pet rogrephic Methods and Cal-c u l a t i o n s " , Thomas Murby & Co. , London, 1921. "The Nomenclature of Pet ro logy" Thomas Murby & Co. , F i r s t pub-l i shed Hay, 1920. "Igneous Ttocks", John ?/iley & sons . Hew York, 1913. "Rock Minora ls , f , John Wiley & Sons, New York, 1911. "Hssently?lF of the Microscopical Determinat ion of Rock-Forming Minerals and ?>ocks", Unive r s i ty of Chicago P r e s s , Chicago, 1922. "Determination of Kock-Poming Minerals '*, John VTiley « Sons, Sew York, 1908, (with S. A. Stephenson) *0n the Accuracy of the Hosiwald Method for t h e Determinat ion of the Hinera le in 8 Rock", Journal of Geology, Volume 27 , Ho. 3 , Apr i l - May 1919. "Igneous Geology of the C o r d i l l -e r » 8 " . Problems of American Geology, Yale Un ive r s i t y Press New Haven, 1913. "Granodlor l te and Other I n t e r -mediate Hocks", American Journal of Science, 4 , Volume 9, 1900 Page 229. "Hydrothermal A l t e r a t i o n of Gran "Formstion of Kaolin a t Moderate Depths", American Itinera lop i s t . Volume 8, Mo. 9, Pages 157-162 , September 1923. Pirsson, L. C. Roeehbusch, H. SohoflelS, S. J. Vogt, J- H. L* Wright, ?» 3!. i i V "Microscopic Charac ters of Vol-can ic ?u f fe" , Ammericsn Journa l of Science (4) 40 , 191-211, 1915, Trans la ted by Joseph l ad ings 'Microscopical Physiography of the Hock Making Miners I s " , John Wiley & Sons, New York, 1903. "Summary of the Geology of the Crown Colony of Hong Kong," "The Phys ica l Chemistry of the C r y s t a l l i s a t i o n and llagmatio D i f f e r e n t i a t i o n of Igneous Hooks", Journal of Qeology, Volume 29, 1921. *Sch i s to s i t y by C r y s t a l l i s a t i o n " American Journa l of r.oienee. Fourth Ber i e s , Volume 22 , 1906. 1 - THE PETROGRAPHY OP THE HOCKS OP HOHG KOHG -CHAPTER I UROGRAPHY (1) General Geography of Asia "The continent of Asia can be divided into four great physiographic areas. Shelving gradually upward from the low plains of Siberia, the general continental level rises to a gre >t central water-shed or divide which stretches from the Blsok Sea to Behring Ftrait. This divide is not always marked by well-defined ranges running in alignment with the general northeast-southwest direction. There are areas where the strike of the ranges is transverse to the water parting. 'Here lacustrine regions are found. The ranges are not high, seldom over 5000 feet in elevation. "South of the divide the level drops to the central depression of the Gobi Desert, where the average elevation is probably less than 2000 feet above sea level. This de-pression extends westward from the eastern edge of the Gobi Desert to Chinese Turkestan, where it is limited by the great elevation of the Pamir. "South of this enclosed depression are the highly (1) Prom "The Petrography of the Hocks of the Crown Colony of Hong Kong" by Mr. N. P. G. Davis (2) See Figure I, Page 11, from "Igneous Rocks", J. P. Iddin 2 elevated table lands of Tibet from 15,000 to 16,000 feet in a l t i t u d e . These vast Tibetan highlands are bounded on the north by the Altyn-tsgh and Euen-lan mountain ranges and on the south by the Himalayas. "The vast mountainous area s t re tch ing from the Amur r ive r to the Caspian Sea forms the northern boundary of the lowlands of the Arabian, Indian, Siamese and Chinese peninsulas. Bordering the low p la ins of the Amur and of China are the shallows of the Yellow Sea and the is lands of Japan and Formosa, once in tegra l pa r t s of the cont inent . "Between the vest cen t ra l highlands and the coast of southeastern China are s se r i e s of smaller mountain chains with a general northeast-southwest trend of which the Coast Range of China i s on«. "This coas ta l area has b°en depressed so tha t the lower par t s of the main val leys have been entered by the sea, giving a f iord- l ike appearance to the cosst l i n e . This also accounts for the numerous islands which fringe the coast and dot the entrances to the mouths of the great r i v e r s . " Local Geography "The Crown Colony of Hong Kong i s si tuated on the south-eastern coast of China in the mouth of the Canton Hiver, near i*ts northern Ehore^ I t includes the large island (1) See Figure I , Page 11 \ 3 of Lan Tau with an area of 60 square miles and an area of 376 square miles on the mainland, as well as the island of Hong Kong. *"Dhe fine harbour of Hong Kong lies between the inland of Hong Kong on the south and the leased territory on the mainland to the north. ?he psspage inwards from the east is through t^ yee Mun pass and the western portal of the harbour opens into the Canton river* "She islands of Hong Kong and Lan Tau are simply two mountainous ridges rising out of the sea to the heights of I860 ana 3000 feet respectively. The general trend of these two islands is northesst-southwept, conforming in general to the structural direction of the whole region. The city of Victoria is built on the lower slopes of the north flank of"the island and faces the harbour. Across the harbour on a narrow promontory on the mainland lies the city of Kowloon at the foot of the Kowloon hills. 1800 feet above the Pea." 4 CHAPTER I I -rGmWBkli C50LOGY--Geology of Asia "An examination of the geo log ica l map of the world w i l l show t h a t the Canadian-Balt id ^rchaean province forme the p o s i t i v e land mass to the nor th-west of the A e i s t i c -European bae in of sedimentat ion or negat ive land mass. So the s o u t h - e a s t of t h i s bas in l i e s a former p o s i t i v e land mass t a i l e d Cathsyeia by Grabau, which a t one time formed a border land t o the s o u t h - e a s t of the bas in of sed imen ta t ion . Csth-ayeia now l i e s beneath the waters of the P a c i f i c Ocean, "Sediments from both these p o s i t i v e land masses were oe r r i ed in to t h i s huge bas in forming the ex tens ive de -p o s i t s of P r o t e r o z o i c , Palaeozoic and Lower MezB*0*0 s t r a t a which now outcrop throughout China and Europe* In p l ace s on t h i s bas in loca l upwarps have permit ted e ros ion to remove some of these sediments so t h a t pa tches of Archaean rocks are exposed in va r ious p a r t e of Chins* "Great orogenic movements dur ing the Upper Llezozoic era laid the fo nidation of the p resen t con t inen t of Asia because no marine T e r t i a r y s t r a t a s re known in Hhina* "These orogenic movements caused the sediment in the bas in to be warped i n t o fo lds which s t r i k e in a nor theas t -5 southwest direction parallel to the present coast line of China from Hong Eong to Mng Pa. "Immense bathollths of granite were intruded simultaneously with the folding of the strata and correspond in strike with the main trend of the mountains so that the bathollths occur as narrow elongated masses. The most easterly of these bstholiths stretches from Hong Kong to fling Po» a distance of about 800 miles and is comparable in else and geological composition to the Coast range of British Coluabis. "The Cretaceous and tertiary of China are represent-ed by continental and marine deposits and it is in these continental Cretaceous strata that the remains of dinosaurs and their eggs have been found in the llongolisn desert* "During the Hlocene period the great moantain f building forces which built the Alps ©f Europe and the Hima-layas,, of Asia simply caused an uplift of the early Tertiary peneplain and renewed the activity of the agents of erosion. Hence the continent of Asia during the Cretaceous and Tertiary periods was above sea l^ vel and undergoing erosion. "The Crown Colony of Eong Hong forms part of the eastern edge of th** great Asiatic basin of sedimentation in close proximity to the down sunken land of Cathaysia. Associated ??ith the sediments which occur in the vicinity of Hong Kong is the largest outpouring of acidic lavas in the 6 world.* Geology of Hong Hong "The oldest rocks are those of the Tolo Channel series consisting of conglomerates, sandstones and argil-lites exposed as remnants in the northwest half of the territory. Inclusions of marble in the Tai Mo Phan eruptive inaioates that beio^ the surface an oiaer formation of lime-stone occurs. Ammonites founa by Dr. Heanley of Hong Kong were examined by Dr. Grabeau of Peking ©ho suggested a Lowe? Cretaceous age for the series, but better material collected by Dr. Williams in the course of the present geological survey of the territory has enabled J. J. Bucktaan to deter-mine the age definitely* It proves to be "Lower Jurassic, Lower T,iast Coroniceratan. These are the only rocks whose age has been definitely fixed by fossil evidence. The Toio Channel series has been highly disturbed, folded, faulted and in places metamorphosed. "The Repulse Bay Yolcanlos have been laid down on the eroded Tolo Channel rocks. They consist of agglomerate tuffs and ash beds. Between Tolo times and Repulse Bay vul canism no disturbe-nce took place sufficient to raise the whole country above the sea, for obscure marine fossils are found in the ash beds. At the south-west end of the Terri-tory, however, what sre apparently Toio rocks were somewhat 7 disturbed before the volosnics were Laid down in then. There is, therefore, a tine interval between. The Repulse Bay Volcanics nay be Upper Jurassic in age. "The extrusion of the above volcanics was apparently accompanied by a considerable amount of intrusion in the form of neokB, Bills ana dykes, that invade*? the Tolo Channel and Hepuleo Bay formations. These intrusions have been called the Tai Mo Shan Series. Volcanic flows continued after some at leaet of cuch unvasions as they are found on the east slope of Tai Mo Shan mountain holding fragments of the intrusives» "The intrusivas vary from quartz-felspar-porphyries to granite porphyries. They have been greatly disturbea, especially in the north-east portion of the area, where they are now schistose and mineralized. The Tsi :!o Shan formation is extensively exposed forming the country rock of perhaps one third of the territory. "Cutting all the shove rocks is a porphyritic hornblende granite or granoaiorite. It has contact meta-morphosed the Tolo nhnnnel rocks and 'he older rocks near its contacts hold numerous quartz veins. It has itself been disturbed and is epidotized along fracturee and joint planes* Its intrusion probably followed a main period of mountain building, possibly the Jurasside Revolution. 8 "Cutting the Taitam formstion is the much more acidic Hong Kong granite. It forms about one third of the country rock of the colony. Due to its mode of weathering as well as its abundance it is much the moFt conspicuous rook* It is cut by aplite and pegmatite dykes that also invade the neighboring rocks. The pegmatites have given origin to quarts veins, particularly in \h(* «rranite itself, containing wolframite, tinstone and molybdenite. "Apart from a little minor faulting and sheeting tke Hong Kong granite sho*/*s no evidence of disturbance except on the north-vest. Here, however, it has been de-formed to gneiss. "Its intrusion was probably the result of the dis-turbcnce that affected the already schistose Tai Mo Shan, the older quarts veins and the Taitsia formation. This may well have been the Taramida Revolution. ''The last important intrusion is thst of the Lan Tau granite porphyry. It variee from pink to dsrk pearl grey in coLor. The composition varies from th>t of a granite to a granodiorite. It cuts the Hong ICong granite against which it has broad s4,rongly marked contact faoies. The Lan Tau rocks have not been altered or deformed. Theyiaarked the IsBt great disturbance, popsibly the Iliocene Revolution. ''Dark grey to black lamprophyre dykes cut all the previous rocks, ?hey are probably d i f fe ren t ia t ion products of^the Lan ?au magma and cons t i tu te the l a s t phase of the igneous ac t i v i t y in the d i s t r i c t . (1) "In addit ion, there are two se t s of rocks whose r e l a t ive ages have not been suff ic ient ly established to place in the above sequence of formations. "Occupying the peninsulas and is lands of the south-eastern coast of the t e r r i t o r y , north-east of Hong Kong i s -land i s a ser ies of lava beds caller! the Rocky Harbour vol -canios. ?he rocks consis t of elongated pink felspar and quartz phenocryste in a reddieh to dark aphanit ic groundmaes. 5he formation i s remarkable for the highly developed v e r t i c a l jo in t ing almost comparable to the basa l t i c jo in t ing of the Geint 'e Causeway,; On the seaward side c l i f f s 300 feet high are c h a r a c t e r i s t i c . Seacaves and stacks are common. Tam-prophyrs dykes are pa r t i cu la r ly numerous in th i s formation. ?hey weather out readi ly , leaving steep walled i n l e t s or vallejis* In several cases the sea has eroded tunnels com-plete ly through the i s l ands . This formation i s cut by the Ian "Pan and overl ies a se r i e s of conglomeratic cuffaceous sandstones and a r g i l l i t e s known as the Junk Bay formation. "¥ae Junk Bay formation r e s t s on the Repulse Bay (1) Br. Brock i s a t present studying the r e l a t ion of these rocks in the f i e ld . 10 volcanics, but holds bowlders of them, indicating a tine break. "After the last period of igneous activity there followed profound erosion- The district wss then subjected to submergence greater than that at prerent observed as evidenced by rock terraces and hanging valleyP. These indicate a sub-mergence of possibly five or six hundred feet greater than now. This was followed by a rising of the Land in stages. Book terrsoos are particularly noticeable at about 480, 350, 800* 100 ana at 50 feet» A small but frequently observed 8«a eilff occurs about SO feet above sea level, A very re-cent elevation is shown by marine shells found a few feet above the present high tide. The coast, however, is still deeply submerged* Mi The facts and inferences outlined above are sum-marized in the following table: ? : I? s >-•; 11 — 'sum -. Recent Pleistocene Pliocene Miocene Laramide Revolution Juraeeide Revolution Upper Juraesio (?) Lower Jurassic — EVEHTS — Upl i f t in s t ages Depression Erosion (Igneous activity (Uplift—Mountain Building (Igneous intrusion , Mountain building (Igneous intrusion Mountain building Volcanic activity Sedimentation —RECORD— (Rock t e r r a c e s (Hanging v a l l e y s Po i rds & Arch ipe l -agoes Mature topography (Laraprophyres (Lan 2au I n t r u s i v e (Rocky Harbour Vol-c a n i c s Deformation of Eong Kong g ran i t e Rejuvenat ion Hong Kong Grani te Deformation of Older Rocks and S t r u c t u r e s faitara formation Deformation and Folding Ts i Mo Shan f o r -mation Repulse Bay v o l -can ic s Tolo Channel fo r -mation 12 CHAPTER III — PETROGRAPHY — Summary of the, Igneous Geology of Hong Kong The distribution of the igneous rocks of China, as conceived by ladings, is shown in Figure I. He states, ^Throughout China the characteriFtie rocks are grsnites, dIoritee and garbbros with porphyries ana some lavas of the same composition. Nephelite syenite has been found on the Yangtze River near Kienohwan and nephelite-basalt at Yangehan, west of Weihelen. Nephelite basalt also occurs in Ilanchuria, northeast of Kukaen* Granites and granodiorites with diorite and gabbro with corresponding lavas characterize the Lias Tung Peninsula ana Chosen (Korea)." The igneous rocks from the colony of Hong Kong vary from granites to granodiorites in composition pnr* exhibit the volcanic, hypabyseal and plutonic phssee. The oldest rooks are pediments snd consist of conglomerates, sandptones end argillitee exposed ae remnants in the north-west half of the territory. They are referred to the Lower Jurassic, Lower Lias, Coronicoratan* (1) The Repulse Bay Voicenice lie unconformably on the Toio Channel sediments. They consist of aoia lavas, quartz-(1) Dr. Uglow oalls this formation the "Volcanic nedinents" . in his field notes. 13 porphyries, agglomerates, tuf fs and ash beds. The extrusion of the Repulse Bay Voloanios was aooompanied by the intrusion of nooks, s i l l s and dykes, The intrusivee vary from quartz-porphyries to gran i te -porphyries and are known as the Tai Mo Shan s e r i e s . The Taitam formation i s a porphyrit ic hornblende-gran i te , which cute a l l the above rocks. (I) The Taitam formation ia cut by the Hong Kong granite which i s an even, coarse-grained, pinkish prey g ran i t i c rock, feat near i t s contacts i t becomes fine grained. I t i s cut by ap l i t e and pegmatite dykes that aleo invade the neighboring rocks. The las t important intrusion i s that of the T,an Tau granite porphyry which i s a pink or pearl grey, highly f e l e -pathic rock, the dominant const i tuent being large felspar phenocryete. Quartz, when present , i s inclined to be id io -morphio, as i s the sparse b i o t i t e . The rock var ies in composition from 8 granite to a granociiorito and in texture from a granite-porphyry to a porphyrit ic r r a n i t e . I t cuts the Hong Kong granite sgeinst which i t has a broad, strongly marked contact fac ias . fl) Ho specimens or field descript ions of t h i s formation were available from Dr. Uglow's map area and i t has therefore been omitted. I t i s equivalent to the DHguilar Peak formation of Dr. Schofield. 14 fl) Dark grey to black laraprophyre dykes cut a l l the previous rocks. They are probably d i f fe ren t ia t ion products of the T*an Tau magma and cons t i tu te the l s s t phase of the igneous a c t i v i t y in the d i e t r i c t . There are too rock groups whose re la t ive ages have not been suff ic ient ly established to place them in the above sequence of rocks• The Rocky Kerbour Volcanics consist of elongated pink felspar and quartz phenoerysts in a rodoish to dark aphanitic groundmass. They are in the main acid volcanics. (2) The Junk Bay formation consists of a basal conglom-(3) erate, containing pebbles of the Repulse Bay Volcanics, with a siliceous and tuffaceous cement overlain by a series of tuffaceou8 sandstones with a few layers of siliceous argil-lites. The Rocky Harbour Tolcanics overlie the Junk Bay formation. (1} Ho specimens available. (2) "Petrography of Hocks of the Crown Colony of Hong Kong" by Mr. H. P. 0. Davis, Pages 22 - 25. (3) "Petrography of Hocks of the Cro**?n Colony of Kong Kong" by Ilr. H. P. 0. Davis, Pages 18 - 23. 15 — The Tolo Channel Series — Distr ibut ion Broadly speaking, there are three areas where the (1) Tolo Channel se r ies i s exposed. On the south-west shore of Lan Tau island the se r ies outcrops from Tai 0 to Sha Lo Vten, a distance of approximately 4.5 miles* The width of the exposure varies from *2 to ,5 miles . The s t r ike of the o beds i s H 30 E. , and they dip a t a high angle to the south-east* Continuing along the s t r ike of the Tolo Channel se r ies on Lan Tau island the beds are found to outcrop on the mainland about 7 miles d i s tan t s t Castle Peek Bay* The se r ies extends north-east for about 8 miles and var ies in width from 14 miles to o.fc miles* That par t which l i e s in the Shap Heung valley outcrops only se isolated patches in the clay deposi ts . The s t r ike of the beds in th i s area i s about IT 30 B, The dip a t Castle Peak Bay i s south-east d't a high Angle while s t tho most north-westerly exposure the dip i s to the north-west a t a h.1 ph angle . This fceiiinentsry se r ies occurs on fhe Brothers between Lan Tau island snd Castle Peak bay. The third area of sedimentary rocks occurs in the v ic in i ty of Tolo Channel and Tolo Harbour, where the out-CD See Figure 2 ! L6 crops represent isolated patches along the shores of the harbour. Llthology Within the area examined by Dr. Uglow, the Tolo Channel series consists of a basal rroup of conglomeratic, qusrtzose, rocks followed by thinly bedded layers of brown-ish, qoartzitic, sandstone with interbeds of sandy, greyish, shale. Argillaceoa8 sandstone, shaly sandstone, shale and some fine breccia are encountered at different horizons in the series* Many of the exposures show a highly fluted weathering* In the vicinity of igneous intrusions these sediments exhibit the effeots of metamorphiem. At Castle Peak bay on the mainland, occurs a slightly contorted netar-glllite, which is- charged with nodules of epidote. One thin section, IV 44, was taken within 100 feet of the contact between the Tolo Channel series and the Hong Kong granite. The rock is a greyish, fresh, eericitic quartzite* A large number of specimens collected by Dr. T.chofield (1) were examined by iir. N. F. G. Davis. His conclusions are quoted here. "The conglomerates of th i s group which were s tudied in t h in s ec t i on are a l l more or le!-s tuffaoeoue in n e t u r e . Liany of them are what might be re fe r red to as non-contempor-aneous t u f f s and may be c a l l e d volcanic conglomerates . The Mr. H. ? . Davis "IThe Petrography of the P Crown Coloay of Hong Kong* ^ a gee 9 - 1 0 . 1? origin and nature of their primary constituents ss apparent-ly igneous, but they are related to exogenetic roclcs by the process of their deposition and by their occurrence in beds intercalated with ordinary sediments* The fragments in many cases have a rolled appearance, but some also show igneous origin by their irregular outline, in some cases showing embayed borders* In them are found, minerals which do not ordinarily withstand the weathering which they would be subjected to in the formation of ordinary detrital sedi-ments whieh points partly to their tuffaceous nature end partly to an extremely, short transportation.* In the tuffaceous conglomerates quartz occurs as fragments of various si2ee, some of which show embayed borders, while oihers chow shadowy extinction indicating shearing stress. Orthoclase and plsgloelaee felspar, show~ ing corrosion, are prerant, but they are much altered to ealeite. Biotite occurs as light brown to reddish brown pleochroic flakes, scattered In between the large quartzes and felBpars. Grains of magnetite and s few prisms of apatite are present. ?he sandstones of the series exhibit transitional phases from the tuffaceous conglomerates through tuffaceous sandstones to the more finely compacted sandstones; in some cases almost quartzites. Quartz containing fluid cavities \ 18 and rutile or apatite inclusions, indicating a plutonio origin, is represented as rounded grains of varying sizes, A few grains of orthoclase and oligoclase are seen. A con-siderable amount of brown, pleoohroic biotite is present with a little magnetite and some zircon* In some sections the quart* grains have been shattered and some muscovite iB developed* fl) Mr. N. P. 0. Davis suggests that the presence of b i o t i t e Indicates that the mineral* have had but l i t t l e transportat ion* Since the Tolo Channel se r ies has been in-truded by Igneous rooks and subjected to mountain bui lding forces since i t s deposi t ion, i t ie not unreasonable to expect to find evidences of both dynamic and thermal netaraorphism in the thin peotions of the rook. The s t r a in shadows shown in the quartz grains , the breaking of the c r y s t a l s , and the a l t e r a t ion of the folspars a l l indicate shearing s t r e s s . (2) In discussing '.hernal motarcorphisra, Harker s t a t e s , "Where a quertzose randstone or r r i t has contained scattered decomposition products, such as kaol in , c a l c i t e and ch lor i te minerals, in small quant i ty , metamorphism produces a ouar tz i t with granules of some accessory mineral . Thus, near the f'hap gran i te , the g r i t s in the GonSston Flags group have been transported into a quar tz i te with granules of colourlesr TTJ Davis, I?. ? . G. "a?he Petrography of the Hocks of the Crown Colony of Hong Kong." Page 13 (21 Harker, Alfred, "Petrology for rtudentsnPage £95, & 38S 19 mioa a t the expense of a lka l i - fe l spars* A cha rac te r i s t i c a l t e r a t i on in the soda-line-felspar*- r e s u l t s in the minutely granular aggregate which has been cal led ' S s u s s e r i t e ' and i s not always of precisely the same na ture . " The f ield r e l a t i ons of the Tolo Channel se r ies strengthen the p o s s i b i l i t y that the presence of a l te red felspar and b i o t i t e i s due to thermal and dynamic metamorphisi Metamorphiem She Solo Channel s e r i e s of sedimentary rocks shows the effects of thermal metamorphism a t i t s contact with the Hong Kong grani te and the ? s i Mo Shan porphyry* In some casei changes in the minerslogical composition of the rock have been Induced through contact with the intrusive plutonic rooks while in a heated condit ion. These in t rus ions were accompanied by the emission of heated gases, vapours and wate] and some of these agencies passed into the invaded roeke and often developed new minerals in thera. Ho hand specimens of thin sections which had been chosen to i l l u s t r a t e the thermal metamorphism of the Tolo Channel s e r i e s were available so that i t i s only possible to br ief ly mention a few evidences of a l t e r a t i o n which were noticed by Dr. Uglow in the f i e l d . Within the contact aureole, the following minerals were developed;- quartz, rauscovite, epidote, garnet and 20 tourmaline* In some instances the sandstones are altered to quartaite or sericitio quartzite. The qusrtzite is sometimes fall of Quarts veinlets given off from the Hong Kong granite. (1) At IV 57, the a r g i l l i t e i s a l tered and contorted a l i t t l e and i s charged with nodules of epidote . At VII 28, the Hong Kong granite i s in contact with the sandstone and a r g i l l i t e of the Tolo Channel s e r i e s . A narrow b * i t , 20 feet wide, against the g ran i t e , ie a l tered to solid garnet, epidote and magnetite. In one instance a fine-grained f e l s i t i c phase of the gran i te , which may be a chi l led margin, occurs a t the contact with the sandstone* From the contact phenomena described above, i t appears that the a l t e r a t i on of the sandstone at the contact in due to thermal, metsmorphism and metasomatism. Structural Helations ^he Cordilleran tr»na in the v ic in i ty of Hong Eong i s nor th-eas t . 2he axis of folding in the 2olo Channel serie roughly follows t h i s o r ien ta t ion . fhe Tolo Channel se r ies which outcrops on the eoutl: west shore of Lan ?au island i s the limb of an ant ic l ine o whose axiB trends N 31 S. 2he dip of the beds var ies from o o 35 - 85 S.E. and they underly the volcanic sedi ents which (1) 1?he numerals refer to the main area l divis ions of the geological map and the small numbers to the individual expoaure a. 21 are exposed to the east. A small synclinal trough occurs at (IF 711 88, 90. 91. The area of this sedimentary series on the mainland appears to be the continuation of the structure occuring on Lan Tan island* The beds exposed at Castle V?*1? bay form o the eastern limb of an anticline whose axis trends H 31 E., while about 6 miles north along the strike, the western limb of an anticline is revealed. The rocks constituting The Brothers iPlands between ton Tan island and the Mainland comprise Dart of a sync line which plunges to the north-east. There are some local disturbances of tho beds due to the intrusion of the Tel Mo Fhsn group and the Hong Kong granite* • The Tolo Channel series is overlain by the Volosnio Sediments (Repulse Bay Volcanice) on Ian Tsu island. An angular unconformity ie evidenced near Tai 0* The series is cut by the Tai Ho Shan porphyry and the Hong Kong granite. The deformation snd folding of the 7olo Channel feries occurred during the period of instability which lasted Trom Jurassic to Iliocene times. (a) "Fossils (ammonites) found by Dr. Heanley of Hong TTJ See large map in pocket. (8) Dr. Brock and Dr. Bohofield "The Geology of the Crown Colony of Hong Kong." 22 Eong were examined by Dr. Grabau of Peking, who suggested a Lower Cretaceous age for these ?olo rocke, but better mater-ial ooliected by Dr. M. Y. r/illiams in the course of the present geologiaal survey of the territory has enable J* J. Buckman to determine the age definitely. It proves to b© Lower Jurassic, Lower Lias, Coronioeratan. These are the only rocks whose age has been definitely fixed by fossil evidence.'* 23 —The Volcanic Sediments--(Repulse Bay Volcanics) Dist r ibut ion Within the area examined by Dr. Uglow, the pr incipal (1) occurrence of the forraation known ae the Repulse Bay Volcsnies i s on the south-west portion of Lan Tau i s land . The outcrops const i tu te perhaps one-quarter of the area of the is land. The f l a t lying a t t i t u d e of the volcanic ser ies i s responsible for the posi t ion of the plateau between l o c a l i t i e s VII 100-104 and X 32, where i t s thickness can be estimated by the fact that i t a lso occupies the bottoms of the val leys aown o Shan Wst. The se r ies i s also especia l ly well exposed ia the vt.lla^B south of Tai 0, around X 104-109 and along the south shore. Lithology The forraation cons is t s mainly of voloanr'c sediments with some closely associated f e l s i t o s and ouartz-porphyries. The bedded volcanics are chiefly quartzose tuf fs varying from fine-bedded ash, g r i t t y ash, thinly bedded cher t - l ike tuff, tuff breccias , breccias and tuffaceous agglomerate. In color they are chiefly greyish to roddinh depending on the number of phenocrysts of auartz and al tered felspar r,hjch are present . The grounfiraass var ies from a oryptocrystal l ine (1) See Figure 3 24 texture to a microcrystal l ine mosaic of quartz ana felspar* Magnetite ana geothite are accessory. Prom a study of five thin sections i t i s concluded that the rocks are quartzose t u f f s . Uocroscopioally, numer-ous angular and rounded phenocrysts of quartz ana felspar are present* Of the quartz* some show embayed borders , while many of the smaller grains show c rys ta l ou t l ines . This i s interpreted as evidence of d e v i t r i f i c a t i o n . Around some of the quarts phenoerysta, which often contain r u t i l e fl) needles, i s a narrow cloudy rim fu l l of small p a r t i c l e s of dark material whose nature i s indeterminable* This seems to indicate tha t a reaction took place between the quartz and the groundraaes* The felspar phenocrysts are al tered to white mica* Araicrocryetal l ine mosaic of quartz and felspar makes up the groundmase. in whieh small amounts of magnetite and goethite are seen. Structural Relations The volcanic s e r i e s i s ee ren t i a l ly f l a t , undulatini a l i t t l e , but not showing any pa r t i cu la r tendency to follow the eordi l leran trend. The lavas show flow structure which : accentuated by the weathering of the rocks* The exact contact of the Tolo Channel se r i e s and t) Volcanic Bediments (Repulse Bay Volcanics) i s not exposed. (I) See Plate 9 25 bat the typ ica l buff sandstone, weathering reddish, with rounded surfaces i s well shown at VII 90 in contact with the quar tz -crys ta l - tuf f of the Volcanic s e r i e s . The Tolo Channel se r ies i s much deformed and the dip and s t r ike of the beds vary. There i s without doubt a s t ruc tu ra l discordance and unconformity between the two s e r i e s . 'The lava flows and associated volcanic sediments l i e in a generally f i s t a t t i t ude o bjtt folded s l i gh t l y along the axis trending N 60 E. The flows along the northern slopes of the island usually dip o o from 10 to SO K« W., while i t i s expected that thoee along the south side dip to the south-eas t . The Tai Mo Shan porphyry has arched the se r i e s of volcanics into an a n t i c l i n e . I t i s impossible to d i f fe ren t ia te the flows from the sedi-ments in mapping on account of the nearly f l a t a t t i t ude of both* Str ikes and dips of the ser ies are indicated on the map where observed. There i s apparently an anni lar unconformity between the volcanic se r ies and the Tolo Channel sediments along the north shore of T,sn 'au is land. Cliffs and r idges eouth of San Chung and Tai 0 are underlain by nearly f l a t - l y ing g r i t t y tuff, with ve r t i c a l pointing. This i s well observed from Tai 0 harbour, where the ser ies ie a t least 900 feet thick and ovorl ies the Tolo Channel sandstone of Tai 0 island uncon-26 formably but the r e l a t ion of the intrusive porphyry to the volcanic se r i e s i s not evident . Near X 93, the 1?ai llo .Shan porphyry may be observed to lap across the bevelled edges of an underlying se r ies of o a r g i l l i t e s ana sandy tuff that dip about 8 30 E. These are believed to belong to the volcanic sedimentary series* Age It Is suggested by Dr* Brook and Dr. Sehofieid that the age of the Repulse Bay Volcanies may be Upper Jurassic. Conolagjone The Repulse Bay Volosnios were derived from a very acid magma* The extrusion of the material was the beginning of the igneous cycle which is represented by the roofers of the Hong Kong petrographic province. This period of vuioanism might be said to be the prelude to the igneous activity which accompanied the great crust movements along the borders of the Pacific during the Jurassic and Tertiary times. 27 —Tai Mo Shan Porphyry— Distribution (1) The Tai Mo Shan porphyry ie exposed ae isolated outorope along the south-east shoree of Lan Tau i s land . A B i l l - l i k e body extends oorapletely across the south-west port ion of the i s l and . This exposure i s about .5 miles in width and 25 miles in length. A large area of t h i s rock occurs in the cen t ra l portion of the i s land . Small out-orope are exposed on the north of Tan Tau island and on Teing I i s land. On the mainland the 2s1 Mo Shan porphyry etretehee from Yau Earn Tau nor th-eas t to Tolo Harbour. The width of t h i s outcrop ie about 8 miles , but i t i s divided by a narrow tongue of Lan Tau porphyry. A smaller patch ie found to the west. Lithology The Tai Mo Shan porphyry is the strati graphic name applied to a group of rocks varying; from granites to ademellite in composition. ^11 the specimens examined are too high in piagioclaee (andesino) to be termed normal granites, while some of the specimens elapsed as sdemellites show a strong granodioritic tendency. The texture of these rocks ranger- from porpnyritio to granitic* The porphyritie character is often strikingly (1.) See Figure 4 28 brought out by weathering. !!he color of the "Jai Mo Shan porphyry varies from a light grey to a dark grey or greenish hue, —Microscopical Description— Phenocrysts She most abundant phenooryst i s fe l spar , which in-cludes both a l k a l i and a lka l i - l ime va r i e t i e s* Of the a l k a l i s e r i e s , orthoclaee and microcline are most abundant, but in some cases a microperthi t ic intergrowth of orthoclaee and a lb i t e i s present . Carlsbad twinning i s very common* l?he a l t e r a t ion of the a lka l i fe lspar produces a f ine , dense, greyish-brown substance which nay be kaol in, but the in-dividual pa r t i c l e s are much too small to allow of eny con-clusive, opt ica l t e s t . ITie a l k a l i - l i ie fe lspar var ies from ollgoclase to andesine. I'he c rys t a l s frequently show a marked zonery banding between crossed nicols end twin-iamellation on the s l b i t e type i s developed. Unlike the orthoclaee, the s l t8 r s t ion products of the plegioclase are of suff icient coarseness to be determined by opt ica l t e s t s . 1'hey are epidote, white mica, oe lc i te and ouar tz . ?he mineral next in abundance to felepar i s quartz in angular fragments or corroded phenocrysts. ?hey are remark-able for the i r unaulatory ext inct ion and the creeks fcy which s t ra in has been re l ieved. Some of the phenocrysts are almost B9 completely reduoed to granules which do not show strain shadows. The crystals of "brown or greenish pleochroio biotite are in tabular plates or lathe, which sometimes show twinning. Occasionally some granular augite is developed• The alter-ation of the fsrromagneeian minerals is to epidote and chlorite- Apatite and magnetite are common accessories, accompanied In some cases by zircon and garnet. Groundmaeg The microcrystal l ina groundmaee of the Tei Mo Phari porphyry cons is t s of a c lea r mosaic of quarts and felspar* In Borne instances, the quarts grains have a feathery appear-ance a t the edges, which may be a t t r ibu ted to r e c r y s t a i l i z a -•i tion. The directive character which the groundmass occasion-ally exhibits is due to the alignment of small flakes of white mica* —The Granite Phase— The granite phase of the Tai Mo"Shan serieB is light grey in color and hypidiomorphic granular in texture. Orthoolaee is the dominant felspar occurring as phenocrysts 4 and in the groundmass. In a few oases a microperthitio intsrgrowth of orthoclase and albite is developed, while andesine is represented by a few large grains. Small graihe of quartz between the laths of felspar make up a large TTJ sea Plate 5 " 80 percentage of the rook. A pale , rreeniah, pleoohroio b l o t l t e , which i s prset ly a l tered to ch lor i t e 1B prepont In ptamll amounts. —Baeio P h i M — In the derk frrmy phea* of prenl ta-porphyry texture largo phenooryata of o l igooleae occur with • few pmeil pheno-oryata of orthoolaae and quarts . The o l igooiaee la a l tered t o white mioa ana epidote , while the orthocleee hae the ueuai dense cloudy materia 1, poeeibly kao l in . The ferronapneeian miners la arc b i o t i t e and hornblende, largely altered to epidote and Jron ore . The groundmepp 1B a mierocry« ,t«ll*na mosaic of quarts and fo leper . —Qnarts-Falspar- Porphyry • Phase— At l o c a l i t y VII 75, t h l e type i s masrive, not laminated and weathere into aub-anguUr bowldere of dul l maroon surface . Microscopically, the totture of the rock IF porphyrit lo . The phenocrypte are orthocispe. showing some mioroperthltle i n t e r -( l ) growth, andeelne and quarts in a raicrocryrttlllr.c groucdmese Of quarts, orthoclape end frequently much white n i c e . The endeelne ir c h i e f l y altered to white mica &nd the cthociase to a cloudy substance, poeeibly kao l in . The quarts phenoorypte hare smooth corroded out l inea or angular edgee. The quarts ( I ) 8 M Plate 10 31 granules in the groondmass exhibit a feathery margin which may be flue to the process of r ec rys t a l l i z s t ion* Ho data on t h i s point was found in the l i t e r a tu re* She ferromagneeian minerals , b i o t l t e and hornblende, are chiefly a l te red to epidote and c h l o r i t e . Magnetite i s accessory* !?he composition of the quartz-felspar-porphyry phase does not agree with tha t of a normal dso l te , but seems to be intermediate between a l a t l t e and a dac i t e . The magma ^roa which these rooks were derived had a composition corresponding to ademelllte ra ther than a true granite or grsnodiorlte* g i fec te of Shearing Btress Host of the th in sections examined showed evidence that the rock had boon subjected to shearing s t r e s s which may hove been applied under two condit ions, in some instances phenocrysts of cuartz and of ferromagneeian minerals are (1) broken and there i s no sign of the groindmass being subjected to shearing stresE* The phenocryets may have been broken when the rock was in motion as a pasty mass. The second condition is when the phenoorysts of quartz and felspar are broken and much white mica, showing a definite alignment, is developed in the groundmass* This may indicate that the rook was subjected to shearing stresr after 5t. had solidified* (!) See Plate 1 32 (1) The effect of shearing s t r e s s on the quartz phano-e rys t s was well i l l u s t r a t ed in a number of cases . 2he c rys t a l f i r s t shows s t r a i n shadows, but as the s t ress i s progressively increases numerous cracks develop and the s t r e s s i s f i na l l y relieved by the granulation of the c r y s t a l , 1?he resu l tan t grains do not show s t r a i n shadows, and in some e#ses flow into crsckfe developed in fe lspar phenocrysts. I t i s thought that the a l t e r a t i o n of the fe lspar Isthe to white mica i s the r e s u l t of shearing s t r e s s as i t wes noticed tha t white mica was developed under stress. . (2) The above ef fec ts have been described by Harker in h i s discussion of metaraorphissi and have been recognised by raeay other workers in t h i s f i e ld , but kn the llorth American l i t e r a t u r e , a t l e a s t , there appears to be few detai led discussions of such phenomena, fhe American occurrence which shows almost sisallar e f fec ts of shearing s t r e s s i s (3) described by Florence Basoom. llie quartz porphyries of South Mountain, Pennsylvania, d i f fer from the 2si Mo Shan porphyries, however, in that the folepars ar3 raraarkably fresh and unaltered* end there i s proof of dev i t r i f i ca t ion having occurred Us-the ground mass, (1) Sao Pluto, 1 (2) Barker, Alfred "Petrology for Students" Pages 320 - 324 (3) Basoom, Florence wS?he Ancient Volcanic Rocks of South Mountain, Penn»'f Bulletin United States Geological Survey 136, Page 4 S3 Metamorphiem In the field there are many evidences that the 2al Mo Shan rooks have suffered thermal and dynamic metamorphisnu (i) I'hess effects, described by Qr» Uglow, are given below* At 103RliV V 12, a deep excavation s^cposes a pink rack which is highly altered and bleached. A banded quartz •ein 4 feet wide snS other veins up to 3 feet wide have a stril of 100 * 5?he softening and bleaching of the 2a 1 Mo Shan porphyry is probably due to the action of these silieious solution. Wear the contact of the Hong Kong granite and the fai Ho Shan porphyry at locality V 14, there is a narrow belt* trending parallel to the contact, of ''hat appears to be white eerleit* schist, probably a contact phase between the two rocks. The contact taetamorphisra was due to the intrusion of the Hong Kong granite* Very liliely the quartz stringers are genetics Ily related to the granite, particularly as they trend normal to the contact. 1?he accompanying sericitization of the *?ai Mo Shan porphyry might explain the deep weathering of the rock exposures* At locality V 87, a tunnel 50 feet long i s driven on the contact of the 2ai Ho ^han porphyry snd B basic phase of, the Hong Kong granite, f'ome garnet and epidote occur in the Tai Mo Shan porphyry. n •• M i i ntaw«iaii*W < X * M > H » ^ . -**••"-•—1—' • M " * m - r • ~r m« n M ti m I i i i "i r 11 • I -i in in i ni l - i i i n i n r • (1) Ugiow, w> L. From Field Notes 34 At l o c a l i t y V 99 . the ? a l Ho Shan porphyry i s o sheared or f o l i a t e d wi th a trend H 65-70 S» , and the rock resembles a q u a r t z - e e r i c i t e - s c h i s t * At IT 135, a small p rospec t tunnel i s d r iven on an S - w shear zone in the £ s i Mo Shan porphyry, near i t s con tac t wi th it tongue of Hong Kong g r a n i t e . This ahear zone, which con ta ins small amounts of e*agnetit@> i s ©hio r i t i zed end sof t* Pro® 1 176 - 179 the 2a i Mo Shan porphyry i s f u l l of rook fragments , n e s t s of en idote and genera l ly shows the e f fec t s of con t ac t raetsiaorphisra. I t appears t h a t the a l t e r a t i o n which i s so apparent i n the !2»i Mo Shan s e r i e s has bsen due to a number of causes* !2he phenocryets developed were broken in many e s s e s while the rock was in movement as a pas ty mass. After the rock had s o l i d i f i e d there wee a period of raountsln b u i l d i n g accompanied by Igneous i n t r u s i o n and the e e r i e s wes acted upon by the forces of both thermal end dynamic raetanorphism* S t r u c t u r a l Re la t ions From X 97 to X 107 the near ly f i s t l y ing volcanic o o sediments d ip fro& 10 B t o HO £ and appear to dip under the t a b u l a r body of f a i ko Shan porphyry to the eas t* At X 93 the ? s l Mo Shan porphyry raay be observed a t low t i d e to lap a c r o s s the bevel led edges of an underlying* 35 o eeries of argillites end sandy tuff that dip about S 30 E and are believed to belong to the volcanic eedimentsry eeries. Hear X 92 the volcanic sediments ere separated from The j?ai Mo Bhan porphyry by a well-marked, normal f a u l t , t h a t c ro s se s a h i l l and i s weathered out i n to a rocky depress ion . 2ha beds of the vo lcan ic sediments bend upwards a t the f a u l t o t o a dip of 80 i n d i c a t i n g t h a t they have been downfaulted. The bogy out l ines ' a s ?e i Mo Shan porphyry in t h i s v i c i n i t y i s a a i n i y « shee ted , quar tz - fe lepar -porphyry t h a t i s bel ieved to have been in jec ted i n t o the volcanic sediments nea r ly con-cordant ly» I t does not show contac t mstaraorphic e f f e c t s or any of the f e a t u r e s of lavs f lows. I t i s believefl to be the ©i l l i n j e c t i o n v a r i e t y of the :'ai U.Q Khan porphyry j u s t as the <3si Ho Fhan -pe^k type i s a plug or neck v a r i e t y and o the r g ran i to id types are dyke v a r i e t i e s . In the v i c i n i t y of X 35 a continuous f e l e i t e and tu f f i s intruded by a l e n t i c u l a r shaped body of r h y o l l t e porphyry which i s an apophysis of the 7ai Mo Phsn porphyry from "Lsn Tteu peak. At Eeyng Fhen, an i r r e g u l a r l y shaped body of 7ai Mo Shan porphyry is vxpoved. ^h i s i s bel ieved to bo e e i i l emanating from the main body a t T«an ?au Fhan and pat 'sing underneath the r i dges to the west to appear again on the Ehore a t X 27 - X 32* 26 At loca l i ty X 46 - 47 the 2al iio Shan rock seems to be a nearly f l a t lying s i l l in the volcanic sediments; i t i s eyenit ic above and grani t ic below. The rhyol l te porphyry, included as a par t of the Tai Mo Bhan s e r i e s , i s believed to be mainly dyke end e i l l in ject ions of viseus , acidic lava, which through movement developed flow s t ruc tu re . The somewhat polygonal out l ines of t a i s porphyry against the Volcanic se r ies (Repulse Bay Volcanics) i s believed to be due to block faul t ing of the se r i e s a f t e r Injection by the rhyol i te porphyry. Prom the s t ruc tu ra l r e l a t i ons i t i s concluded that the f s i Mo Shan porphyry i s a s i l l and ayke phase of the igneous body of ?hich the *'olcenio ftediaents represent the extrusive phase. Age The age of the Jai Ho Khsn porphyry i s placed as Upper Jurassic by Dr. Schofiold und Dr. Brock. 2he ser ies was folded and fsuiter" during the Jurassic Revolution. 37 —Hong Kong Granite — Distribution (1) The Hong Kong g r a n i t e i s Dart of a huge b a t h o l i t h , ex tending from Hong Kong to TJing Po, which i s comparable in e l s e t o the Coast Range b a t h o l i t h of B r i t i e h Columbia, In the map 8rea the g r a n i t e i s exposed In many L o c a l i t i e s fo r v a r i a b l e d i e t s n o e s , but appa ren t ly has not been unroofed as Long a s the Coaet Range b a t h o l i t h , s ince the surface between the i s o l a t e d outcrops a re composed of o lde r rooks and ropr«»H»nt roof pendants which have not ye t been eroded. On the mainland, north of Hone Kong i s l a n d , the Hong Kong g ran i t e i s exposed from the v i c i n i t y of T*yee liun Pass a long the shore of Eowloon bay and n o r t h - e a s t to Gin Drinkers bay. This exposure con t inues in a n o r t h - e a s t d i r e c -t i o n to Tide cove . To the west the g r a n i t e again outcrops on the shore a t Ting Kau and extende to ""isrtle Peak bsy . This ounorop con t inues inland for about 4 m i l e s . e s t of Cas t le Peak bay the Hong Kong g ran i t e i s found along th<? phore of the peninsula to rha Kong Uiu, a d i s t ance of 11 r : i l e s . The aae te rn boundary of t h i s exposure i s roughly o s t r a i g h t l ine Join ing VII 71 and IV 54. ?o the west of t h i s body on the mainland l i e Tong (1} Sao Figure 5 38 En island and Pan Chan i s land, wholly composed of g ran i t e . A email area of granite i s exposed on the west shore of Tan Hsu island from Bha Esin '2an westward 2.5 miles with a width of ahout I n i l e . On the south-east side of Lan Tau island the granite occupies a small peninsula and Ch'eung Ghau i s land . 1'he south-east half of Hi Ku Chau island i s made up of Hong Kong gran i te , while small exposures of granite occur on the north-east end of TMZi. ?au island and on Ma ?ran island and ?eing I i s land. Tdthology Ifhe typice l Hong Kong granite ie coarse-grained, holoerys*;alline, equigranular and l ight pinkish in co lor . t?here a r n , however, many modifications' to finer-grsinert and darker-coloured v a r i e t i e s . Dr. Brock s t a t e s , "Due to i t s rac^de of weathering ap well as i t s abundance, i t If much the moet conepicuons rock. I t i s normally an even, coarse-grained, pinkish, grey, b i o t i t e g ran i te , but near i t s contact i t beoosies fine-grained. I t i s out by ep l i t e and p a m a t i t e dykes that 8lso invade the neigh-boring rocks. ?he pegmatites have given origin to ouartz veins pa r t i cu la r ly in the granite i t s e l f , containing wolframite t instone and molybdenite.'* For field purposes th i s rock group was termed a 39 granite* A study of the th in sect ions , however, revealed the fact that the mineralogical composition var ies from s granite to e granodiori ta . Of the specimens classed as gran i tes , a l l were found to be too high in plagioelsee to be called normal g ran i t es . *Phe texture var ies from porphyrit io to grani t ic and a laost ephani t ic . fhose specimens which tend towards granite in eoiapoeition are l ight grey or pinkish in color, while those which have more the composition of granodiorite ere dark prey* Mineralogical Characters Quartz i s seldom isomorphic , except where enclosed by raicroellne and freauen*;ly shows inclusions of r u t i l e needles The dominant felspar i s usually orthoclase, in which Carlsbad twinning i s common and the a l t e r a t i on i s to a f ine , dense, cloady material which may be kaol in . Ilicrocline i s quite frequently seen and i s abundant in some specimens. ?he plagio-clase felspar i s oligoelase or andesino and the a l t e r a t ion i s to white mica and epidote. Brown, pleochroic b i o t i t e i s common and green hornblende occurs, while minor amounts of granular augite are sometimes present . Apatite i s a common accessory, with zircon, garnet and magnetite. Lllcrographic intergrowths are often peen. 40 —'The Fine-Grained Phaee Microscopically, the fine-grained phase of the se r ies cons is t s of minor numbers of phenocryete of quartz, orthoclase and plagioclase (andeEine). Some raicroperthitie intergrowth of orthoclase and a lb i t e occurs, ?he groundraass ie usually a microcrystal l ine nosaie of quartz , orthoclase and p lagioc lase . Ferroetagnesian minerals are generally absent. Very l i t t l e micrographic intergrowth i s seen se a ru le but one specimen proved to be a granophyre, being almost com-ple te ly composed of an intergrowth of orthoclase and quartz . —The Granite Phase— In the hand specimen the granite phaee of the se r i e s i s pinkish in color . *2!he texture i s coarse-grained and in some oases gneieeie banding i s shown. A thin section of such a gneiesic specimen wss examined* and i t was found that the quartz phenocryete show (1) the effects of shearing s t r e s s . Many large phenocrysts have been broken into a great number of closely compacted granules. She large fragments which have not relieved the s t r e s s by breaking, show s t r a in shadows, but the small grains do not show these opt ica l anomalies. In some cases the small granules of quarts appear to have penetrated cracks in the (1) Plate 5 i l l u s t r a t e s s i n i l a r s t r ess ef fec ts in the 2ei Mo Shan rocks. 41 fe lspar , The fe lspars are orthoclase, showing a great deal of microperthi t ic intergrowth, and o l ig ioolase . Some anortho-olase was not iced. The fe lspars show two d i s t inc t a l t e r a t i o n s . The f i r s t i s to a dense, brownish eubftanoe, which may be kaolin ana superimposed on t h i s i s a second a l t e r a t i on to white raica* The ferromagnesian minerals ere completely al tered to chlor i te* This type of g ran i t e i s an example of a strong or highly r igid rock subjected to shearing s t r e s s . In th i s eaee the s t r e s s i s relieved by the individual minerals breaking and a l t e r i n g while the rock as a whole remains r i g i d . The felspar under shearing s t r e s s has a l te red to white raica. The f i r s t , brownish a l t e r a t i o n may have been due to pneumato-ly t io processes, —The Aaemelllte Phase— The ademellite phase of the Mong Kong granite i s pinkish' in color and hss a hyp isomorphic t ex ture . I t i s distinguished from the granite type in the hand specimen by the larger percentage of creamy to greenish colored plagioclase which i s in contrast to the pink or thoclase . The plaf^Loclase i s andesine and i t i s frequently a l tered to white mica and epidote. The ferromagnesian minerals are pa le , yellowish-brown, b i o t i t e and hornblende a l t e r i ng to epidote and c h l o r i t e . —Oranodiorite Phase— The granodiorite var ie ty i s 8 greyish rook which 42 has a larger percentage of forromagnesian minerals than i s found in the previous types . Andesine, a l t e r i ng to white raioa and epidote i s the dominant fe lspar , but orthoclsse i s present in subordinate amounts. Large phenocrysts of quartz which show the effects of s t r a in are pre r en t . The ferromagnesian minerals ere almost completely a l tered to c h l o r i t e , i'ome color less to greenish-brown flakes of b i o t i t e (1) occur, which have bent under shearing s t r e s s . I l lmeni te , surrounded by a border of sphene, 5s present* Contact Phenomena In many instances a f ine-grained, f e l s i t i o phase of the grani te l i e s against the sediments which i t intruded. •?his appears to be a cooled or chil led margin. At loca l i ty (2) IV 42, the marginal phsee of the Hong Kong granite i s strongly foliated close to the oontact with the sediments. In the contact zone occur granite-porphyry, com-plementary dykes and knots of pegmatite. These appear to be d i f fe ren t i a tes of the main body of Hong Kong gran i te . Structural Relations Apart from a l i t t l e minor faul t ing and sheeting, the Hong Kong granite sho^s no evidence of disturbance except in the north-west. Here i t has been deformed to gneiss . In the field th i s se r i e s Is seen to intrude the ?olo Channel fl) Plate 2 shows a similar case noticed in the ?ai Ho Shan porphyry. (2) See Plate 8 43 s e r i e s , the yo lcan ic s e r i e s ana the Tai Mo fihan prophyry. The Hong Kong g r a n i t e i s cut by the Lan *3?au porphyry. £J6S Dr» Sehofield and Dr. Brock "believe the intrusion took place during the t&rsmide Revolution. 1!he intrusion of the Hong Kong batholith marked the height of the igneous activity which, acting with the contemporaneous mountain building, tended to relieve the accumulated stresses in the earth's crust along the south-east coast of China. 44 MIHERALOGICAL COMPOSITION OF KOHG KONG GRANITS Planlmeter Method # 77 38 # 60 # 50 Quartz Orthoclaee Plafioolsse Plagioclase Orthoclaee Quartz Ferromsgneeian minerale Plagioclase Orthoclaee Quartz Ferromagnepisn minerals Plagioclase Orthoclase Quartz 29*3£ 23,2 47.4 51.2 22.7 19*1 6.9 54, 17, 15. 11, 50, 32, 22, • 6 .9 ,6 .0 .8 .3 ,9 Granodiorite Granodiorite Orsnodiorite Aderaellite 45 # 48 #229 f» S, Plag ioc la se Orthoclaee Quartz Pe rroma gne s i an minera l s P l ag ioc l a se Orthoclaee Quartz Perromagnesisn minara le P l ag ioc l a se Orthoclase Quartz Ferroiaagnesian minera l s P leg ioc laee Orthoclase Quartz Ferro&iagnesian mine ra l s 14,5^ 38.4 40.4 4 .0 32 .3 £9 .1 18.2 6 .1 22-.4 28,2 46*4 .5 29 .1 44.2 22 .3 2.6 Granite Grani te i d e m e l l i t e Ademellite 46 —1?he Tjan T»fl. Porphyry— Distribution . . The T»an ?au porphyry iB exposed on the moet south-westerly t i p of r&n Taxi island and on a email peninsula three miles to the west. ?he islands fringing the south-east shore of Tjan Taxi island are composed wholly or in pa r t of T*an Tau porphyry. The rock cons t i tu tes the north-east half of lien Tan island and over half the area of Telng I island* On the mainland, a narrow tongue ertends frora the shore at l?susn Wan nor th-eas t , a distance of about 4 miles- The average width of t h i s exposure i s .3 miles. On the shores of ?olo Channel the T,an Taxi porphyry i s ex-posed a t Tal Po Market and extends south-west for 6.4 miles with an average width of .6 miles . Tjlthology The Lan Taxi porphyry var ies in color fxoa pink to dark grey. In composition, the rock varies from a granite to a granodiori te , while the texture varies from a quartz-felspar-porphyry to a porphyrit ic grani te . The rock i s highly weathered on the surface end the phenocrysts of felspar and quartz stand out in r e l i e f in the granite porphyry phases. (1) See Figure 6 47 —Porphyritic Phase— The porphyri t ic var ie ty of the Lan Tau ser ies i s designated a quartz-felspar-porphyry. Megascopically, the rook i s pinkish in color , with small phenocrysts of orthoclase and quartz in a dense matrix- In the thin sect ion, pheno-crys ts of quartz , orthoclase and plagioclase occur in a microcrystal l ine mosaic of quartz and felspar . Considerable ©lerographio intergrowth i s frequently preFent in the ground-raass. She quartz phenocrysts are generally corroded. The fe lspars are a l tered to white mica and epidote, while the ferromagnosisn minerals are frequently almost completely al tered to ch lo r i t e and epidote . Apatite and magnetite are accessory. —Granite Phase— One phase of the "tan Tau porphyry approximates granite in composition. The rock is flesh pink in color and hypidiomorphic granular in texture. Quartz constitutes about 10>3 of the ?9ek, but occurs as small grains between the felspar crystals. For this reason it is not noticeable in the hand specimens and in the field the rock has monzon-itic character^* The chief felspars are orthoclase and cticro-cline. A small percentage of andesine is present. Ortho-clase and microcline are altered %% § fine, dense, cloudy materia 1. The endesine is altered to white nlca and epidote. 46 The ferronagnesian minersIs occur in minor amounts, but they generally a l t e r to ch lor i te and epidote . Some al tered b i o t i t e with prisms of apa t i t e in i t occur. —Adera© 1 l i t e Phase— The ademellite type i s a porphyri t ic rook of pale flesh-red co lor . Plash-red phenocrysts of orthoeisse up to »T6 laches long, showing Carlsbad twinning, with some white fe lspar ooour in a medium-grained matrix of hornblende, felspar end quar t s . The orthoclase i s almost completely al tered to a f i n e , dense, cloudy material and forme a large percentage of the rock. The plagioclase felspar i s sndeeine which i s a l te red to white mica. Quartz i s present in small grains between the fe lspars and in the groundraass. Hornblende and b i o t i t e are present in minor amounts and show a l t e r a t i o n to ch lor i te and epidote . Apatite and magnetite are accessory. The terra ademellite i s applied to t h i s rock beosuse i t con-ta ins too much plagioclase for a normal granite and too much quartz for s normal syeni te . I t i s intermediate in composi-t ion between a granite and a granodiori te . —Granodiorlte Phase— The granodiorite phase of the Lsn Tau i s pinkish grey to dark grey in color . The texture var ies from graHQ#4;io to porphyr i t ic . The r a t i o of orthoolase to plagioclase feleper corresponds f a i r l y closely with that given by 49 ( l ) Lindgren in h i s descript ion of granodior i te . A large percentage of quartz i s present as sub-hedral gra ins . Large phenocrysts of andesine largely al tered to white mica are present . Orthoelase i s noticed in minor amounts and shows the usual cloudy a l t e r a t i o n . Some micro-pe r th i t e i s found. ?he ferroraagnesian minerals are horn-blends and b l o t i t e , a l tered to ch lo r i t e and epidote. 2he groundmsse i s generally a mosaic of quartz and or thoelase . Some specimens seemed to have a l i t t l e too much qaartz and plagioclase to be normal granodiorites* Contaot Phenomena At loca l i ty VII ( l ) , in the sdemellite phase of the T*n Dau rooks, quertz-felspar-pegmatite bundles and ve in le ts occur, accompanied by some glassy quartz v e i n l e t s . Galena and some sphaler i te occur with these in the heart of the porphyry. The sulphides may be a phase of the pegciatic uprser contact zone of the porphyry. A W i l l 8 quartz occurs in crus t i f ied veins with brownish rock fragments between the v e i n l e t s . 1'his nay be a replacement in sandstone, under contact condit ions, from the Ian 2au porphyry. At VITI 61 a small amount of galena i s scattered through the Hong Kong granite near a small shear zone within f i ) Lindgren. W. ^ ^ g l n ^ S l n i ^ o J ^ B r e n g S ^ ^ o f u l e ^ ? ^ " 1900, Page 229 50 25 feet of where the Hong Kong granite Is cut by the Lan TaU porphyry. Galena, sphaler i te and chalcopyri te , a l l occur without any gangue, in seams in the Hong Kong granite and in pegmatite nests in i t . The minerals appear to be related in or igin to the pegmatite, ?/hioh may have resulted from the i^jbrusion of the Lan Tau porphyry in the general TH5-FW % one of weakness. St ructural Relatione The s t ruc tu ra l iirend* of the region i s north-east to south-west and the Lan Tau porphyry i s a l en t icu la r shaped mass with i t s long d i rec t ion pa ra l l e l to the s t ruc tura l d i r ec t ion . I t cuts the Hong Kong granite against which i t shows ohil led margins. At many l o c a l i t i e s i t outs t.he Hong gong granite in, the form of dykes. There i s a mult inl- s i l l on the extreme south-west shore of Lan Tau is land, which dips about H 30 K through the lavas and associated sediments. In the rent rant a t X 47 the <1ip i s well shown. .'he mort north-espt portion of the multiple s i l l i s a granite porphyry with t rachyt lc fe lspars oriented probably p a r a l l e l to the contact. The next s i l l i s a fine-grained granite which i s mapped as Hong Kong gran i t e . The mort south-westerly s i l l i s of Lan • -Tau porphyry. E>1 I t i s probsbJ.e that those s i l l s as well as the intrusive body of X 14- X 19 are apophyees from s body of T.an 1?au porphyry and are tabular bodies invading the vol-canic e* From X 46 - 48 the rock appears to be a nearly f i a t - ly ing s i l l in the voleanics. Age fhe Lan ?ea rocks have not been subjected to stress and t he i r intrusion narked the les t great disturbance in the v i c in i ty of Hong Kong, possibly the Iliooene Revolution. -* 52 KINSRALOGICAL COUPOSITIOH OP LAN TAU PORPHYRY X 54 V D V 86 X 15 V 557a P l a n i m e t e r Llethofi P l a g i n o i a e e Orthoclap© Quar tz Pe r r oaa gne B i a n m i n e r a l s P l a g i o c l a s e Q r t h o c l a s e Quar tz Perroma g n e e i a n m i n e r a 1 B PlBgiOClEOe Orthoo la pa Quar tz Perroraagneeian m i n e r a l s P l a g i o c l a e e O r t h o c l a e e Quar ta Pe r r oma gne s i a n m i n e r a l s Anflesine Q r t h o c l a s e Quar tz Per romagnae ian m i n e r a l s 9 . 6 £ 74.. 4 10.0 6 . 0 4 6 . 7 18 . 29 5 . 5 5 . 1 7 . 3 8 . 8 . 17 . 6 3 . 1 8 . 2 . 4 3 . 5 15 . 3 0 . 10 .4 G r a n i t e Granod i o r i G r a n o d i o r i A d e m e l l i t e Granodiorite 53 CHAPTER IV —SUMMARY AND CONCLUSIONS— (1) According to Harker, the normal cycle in which igneous activity manifests itself is: (1) volcanic phase (2) plutonio phase, (3) minor intrusions. The rocks of the Hong Kong province are a good illustration of a complete cycle of igneous activity. The Volcanic sediments and the Tai HO 8han porphyry constitute the volcanic phase. The Hong Kong granite and Lan Tau porphyry represent the plutonic phase, while the dykes which out the Hong Kong granite and Lan Tau porphyry are the minor intrusions* It appears that up to the close of Lower Jurarsic time stresses had been accumulating in the earth's crust along a direction which corresponds to the prerent coast line of China. The accumulated strorsee were relieved in two ways—"by igneous intrusionr, which the Hong Hong suite of rocks represent, snd by crust movements of the mountain building type. The igneous activity began in the Upper Jurassic, reached its maximum development during the Laramide Revolution and died away at the close of Miocene time. From a chronological standpoint, the rocks of the Hong Kong province are assigned to the Tertiary period of activity (i) Harker, A. "Ulatural History of Igneous Rooks" Page 97, also see Figure 2 Lirn-ps OF T H E pRirrci fML P A R T OP THE- FfcciF/c P C T R P G R A P H I C A L R E G I O N FOR THE TERTIARY AND RECENT JGNE'OUS RotKS Frtm Ha^*r't rinru/-a( Pt3rory or 2'qntstjt >uxAj "97 FIGURE Z 54 in contrast to the igneous rooks of Palaeozoic and pre-Palaeozoic age. (1) From a study of Barker's chart of the petrographic regions we would expect that the rooks of the Hong Kong province would have the general minerslogical characteristics of the Too&e of the Pacific region. These are: fl) Alkali-felspars, not abundant, except in the more acid rocks and wanting in the basic, soda lime felspars abundant. (2) Zonary banding of felspars frequent. (3I Felepathoid minerals not found. (4) Quarts not only In acid rooks, but also in many intermediate ones. (5) Pyroxenes represented by sugite„ diopside, end the rhombic group; amphlbolee by common hornblende. i6) Miea not common except in the more acid rocks. The,mineralogies! composition of the rocks varies from that corresponding to a granite to ademellite and grano-dlorite. Only one example of normal granite was studied* the rest of the specimens classed as granite in the field, being rather high in plagioclase to be typical examples of that rock type. The dominant rock type appears to have the composition of quartz monzonite and was called ademellite. The plutonic rooks, i*e., the Hong Kong granite and Lan Tea porphyry, ere the crystallized equivalents of fi) See Figure 7 55 large "bodies of deep-seated magmas* These invaded the stratified Tolo Channel series, not in one advsnoe probably, but by repeated advances of liquified rock. The Lan Tau rock cuts and sends forth apophyses into the Hong Kong granite. The intricate relationship between the successive intrusions (1) is shown in ?sing I island and on the north end of Lan Tau island. There a re many l o c a l i t i e s where the roof has been l i t t l e sore than removed, the p iu ton ic rocks exposed a t the surface being laden with fragme-nts of the s t r a t i f i e d s e r i e s a s t r u l y aa when they are in l a t e r a l contac t wi th a roof rem-n a n t . 1?he c lose raineralogical r e l a t i o n s h i p which these rocks bear to each o ther sugges ts t h a t the d i f f e r e n t i n t r u s i v e bodies were produced by the d i f f e r e n t i a t i o n of a magna tha t must have been a t l e a s t of homogeneous c h a r a c t e r . One of the most i n t e r e s t i n g f e a t u r e s of the rocks of the Hgng Kong s u i t e i s the a l t e r a t i o n of the f e l s p a r s and ferro-marnealan mine ra l s . This a l t e r a t i o n was a t t r i b u t e d by (2) Mr. N. ? . G. Davis to the agencies of weather ing. In many c a s e s , however, i t appears t h a t the a l t e r a t i o n nay be due t o thermal and dynamic metamorphism. In comparing the Hong Kong b a t h o l i t h with the * (1) See map in pocke t . (2) Davis, If.P.O. ' 'Petrography of Rocks of Hong Kong",Page 30 56 Coast Range batholith of British Columbia, Davie etatee— "Hence ite (Hong Kong batholith) more cid nature is what would be expected from the crystallization differentiation of a magma and its age." Davis believed the Kong Kong batholith to be granitic in composition, but all the specimens available show its distinct granoflioritic tendencies. Ke also overlooked the fact that the Coast Range batholith ie made up of a number of separate intrusions and in some oareB it has the composition of granite. Along the fiords of the Coast Range, exposures of the batholith may be seen v extending from sea level to altitudes of 8000 feet. Dr. (1) Doloadgo, in his study of the bstholith, has found no regular gradation from acid to basic composition as a de -per part of the batholith is reached. It seems only possible to state that both of these batholiths belong to the Pacific Region of igneous rocks and hence have the same general mineralogi-cal characters exhibited by all the rocks of this region. (1) Doimadge, V. Personal conmunication —LIST OF ILLUSTRATIONS— 1* 5a1 Mo Shan Porphyry, i l l u e t r a t i r g e f f e c t s of shear ing s t r e s s . P l a t e 1 . 2. Tai Mo Shan Porphyry, I l l u s t r a t i n g effects of shearing ntrocs . Plate 2 3 . Sal Ho Shan Porphyry, i l l u s t r a t i n g ef fec ts of shearing s t r e s s . Plate 3 . 4* Tai Mo Shan Porphyry, i l l u s t r a t i n g ef fec ts of shearing s t r e s s . Pis te 4, 5. Tai lio Shan Porphyry, i l l u s t r a t i n g ef fec ts of shearing s t r e s s . Plate 5 . 6. Tai Ho Shan Porphyry, i l l u s t r a t i n g effects of shearing s t r e s s . Plate 6. 7 . l»ai lio Shan Porphyry, i l l u s t r a t i n g effects of shearing s t r e s s . Plate 7. 8. Hong Kong Granite, i l l u s t r a t i n g ef fec ts of sheering s t r e s s . Plate 8. 9* Volcanic Sediments, i l l u s t r a t i n g zone around quartz phenocryst. Plate 9. 10. Hong Kong Granite, i l l u s t r a t i n g raicropegniatitio intergrowth. Plate 10, PLATf T A 4p<i+it«. 3iidr.*<s-£. ~ai Ho 5/>dn Porphyry. A. 6 0 ' ( %t "Biohtc HAS broken under <3b<ann<2 =*tre?5 i>uf ton ,s no Sl«r> o f +he oreundma** kd ".^n been Subjected +*> 3 Similar force. -PLATE Z L v A X 6 0 ' A la/Hi of tnot i t i vh '^K W y been oliqAt/y t w f due h gteannj cS+rt J J. r PLATE 3 0 i 4 * r t i 3«t.on ^ X 5J "TV. fOo 5A«n 'Rfpfcyry X 6 0 PLATE 4 "Section ] y 51. T<3» f^o 5*>an Torpfiyry-X 6 0 A ?h attend pbenocry^f- o f qoarfe 3Wi i< j 30mt of ftt. grains penct"r*f"w a crystal o f tclspar. r L PLATE 5 "1 A Sec+-10o "ST 4 9. T a i f \ o Shon Po rphy r v X 6 0 rphy y ancl then l>n|ftn mt» f\bmtrous small oranu^s. PL/\TE 6 r "i A i*Uqnrvv«r\f.<-(uc "ft Section T -4 I - "ai ^Oo "3IW\, PorpAyrv. ~Tfe a n w i d m u f Us *.««».td <* rf«fi.ft -/M^m»nf U/id«r *W,/>} c?t««. PLATE 7 r 1 J AuarilL WSitt. Imica. "Biot^t 5*'t'un r w X 6 0 PU-tc t» l/ lujrtratc * t dmcttrc c W < * c f t r of Hit Qr°und rnajs «*d Kie. ^ . v d y n ^ f - of fla&s of bum around the. p^i«ocry^fj oF<iu«rt2 «/\ri felspar. PLATE 8 r L ^ c f i o n W ^ l . "1 J X Zbf noi\q Kono Granite Xllus-fro^io^ of a- rocK' h/dicK A«j ajKip|e-(s(y yieldecl to ^/ica.'-i"? ^tr-t^ cir*d mry*f*llizaho* of the. minerAU has f^r, place.. PL/4TE 9 r L ^ A ill »crocn/J W l ' ^ t y^tLSaic of4Ut\r^_ 5et+/0H A S» 3 Volcanic J>Cc( ly^t n~tf. X Z64 A hybrid 2-Ont } ^tck could n a f At Mtrt*ir,ul optically , ex isfaj <3La.rt2- p ' lcnccrvs ' f? ground Cc> PLAIE 10 ' Orthwlwf Quartz XL xh H O Q Q \fonG{ GraA\tz. YZW Q r W k » t . 

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