Sketch of the Geology of Co. Antrim
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PROC. GEOL. Assoc., vol. XIV. PLATE V. a. b. a. c. b. g§ f. =~ '-" l .f. J - ~~" ' ~ .;: g. g . Shc!ls. h~ ) ul)" , ,,/94. + Places where recent shells ha ve been found. She lls found 9 fee t to t riuht, in a face ncarlr at rightangles to thissection . BRIGST OCK SECT ION - LINCOI.NS HIRE OOl.!TIo: AN Il DRIFT. (.Showr;lg positions ill ll·hich Land IIl1d / ·j·esh-1('(lt"" shdl, wen j;rllld by .1/1'. Albert IFlllli' .) a, a . Soil to bro wn drift, with few sto nes a nd bould ers, h, b. Brown clayey drift. with many boulders (oolit ic and flint and cha lk predomina ting) , Boulder-clay. t", c. Sa ndy clay in bands with out houklers ; probably d isturbed Upper Estu arine cla y. d. Distorted Oolite an d Boulder-clay, much con fused . e d i s t r i b u t c d e. I ~ Oolite in sma ll stratified bed s, with flint and oolitic water-worn stones and rece nt shells -i-oftc n distor ted. .f. Disintegra tcd Ooolite with large lump s of hard oo litic rock . g. Floor of q ua rry. ( Seal,· : ()ftd /0 th~ ill(h. Lm;;th ofSection 36 p d.) To face I'W' US·I PROC. GEOL. Assoc ., VOL. XIV. PLAT E VI. N OTE.-TlJis map is jJY;lIteti all f ape ,..suitable for usater-co/our, Ttie narrow nnsttadcd a1'cas on tlu: coast at IV/d fe Pa rk Bay, and on either side 0/ Garron Poin t, an: L ias. SEDIMENTARY ROC KS. EJ~ Cretaceous (Chal/; f/lld Greensand), I~ L iassic ( Lou-cr Lias and Rhb"tic). Triassic (,\ '''<' Rcd .'/llldstOIlC. we ~ 41 Bunter, and Kcufrcr), ~ r L'- c:IJ Permian (So uth S IIOI 'c of Rdf ast 4. ~~~ ',,"/" L 01~!;h ). ~jv ,,~ ,"1 ~ ~ : · t. IJ f l ~1 : : Carioni" fcrons. t:x-""o-.q:-·1. Lou -cr Old Ned Sandstone. I? :S';] SiluriaII aru] Ordouician. ~ ,l/etamorphic (J l i,'a Schist , (j uarl:. S c/ust. L imestones, etc,' , IGNEOUS ROCKS. Tertia ry Ram ll s ( t.:pp ,·r am CJ L O<i'cr ), AII)'olil,·. ~ , I+·.~;.."+';to l (jU/lrt::-porpll),ry. ¥.' .2Ja /Iynw »ce c y r ,1/icro<Trallil,' [ill\' \r .~ ~ 'Jj $) .J1"t UL-'mifJv s 771cUll rru ; v A NE:CI( 1° 7 ~ ' ' .J3tl l{C/7'rz.l/YUV <:X> Z;U -ti7' t e: . ~ ·.7J(t tll/ d4r" ~ if. liS ~.. ' A ·,,:: ~ ( (~ ." . 7/1?1~fl/t7-l~k ?'o zl'" L ou.!Jh- JVR..ajllv. GE OLOGICAL MAP OF CO UNTY AN TRDI, ;\ . By A. ~ IcIlE:\RY ~I. R , I. S(t"~' 4 11.tI, J 10 t I I1( h. o ~ k:d (R educed trcu . the cr.e-inch ..lu et -,of th e ( ; l: t) l ~1lI \t.) . ) 129 SKETCH OF THE GEOLOGY OF CO. ANTRIM. BvALEX. McHENRY ~I.R.I.A., ofthe Geological SZI1vey ofIreiand, Read 5th Juty, I895.) HE County Antrim is particularly interesting to the Irish T geologist, as within its bounds are to be found representa tives of almost every geological formation that occurs throughout Ireland. Beginning with the older formations, we have, in the northern portion of the county, in the neighbourhoods of Cushendall, Cushendun, and Ballycastle, the foliated crystalline rocks, the age of which is at present unknown, though they probably' belong to a period not later than the Ordovician; while immediately on the south-east of the county, in County Down, the Ordovician and Silurian strata occur in great force. At Cushendall and Cushendun there is a considerable extent of Lower Old Red Sandstone rocks, consisting of massive pebble conglomerate, sandstone, and shale. In the extreme north of the county, at Ballycastle, and extending round Fair Head beneath the dolerite, to Murlough Bay, are to be found representatives of the Lower Carboniferous formation. The Permian rocks do not appear at the surface in County Antrim, but a few miles to the north-east of Belfast, on the south shore of Belfast Lough, they occur in close proximity to the Lower Carboniferous and Triassic rocks (New Red Sandstone). The Trias, consisting of the Bunter and Keuper divisions, occurs in considerable extent throughout the county, especially in the southern portion of it, where it attains a maximum thickness of over 1,000 feet. In the north of the county, however, it dwindles down to but a few feet, as at Torr Head and Murlough Bay. The Rhsetic Beds occur generally in the south and south-east, the greatest thickness being in the neighbourhood of Lame. Lias is well represented at several places, notably at Lame and Island Magee, and in the north at White Park Bay and Portrush. Cretaceous rocks, consisting of Upper Greensand and Upper Chalk, appear from heneath the basalt plateau almost continuously round the whole county on its north, east, and southern boundaries, and extends into County Derry on the west, its general position being at the base of the basaltic escarpment. Capping all the other rock-formations, and almost completely covering the whole county, is the great plateau of Tertiary Basalt, indicating two well-defined and distinctly separate periods of volcanic activity. The Period of rest is defined by the remark able and important deposit of the Pisolitic Iron-ore zone, and its associated plant-, ash-, bauxite-, and bole-beds, AUGUST, 1895.] 9 13° ALEX. MCHENRY ON Boulder Clay is very extensively and generally distributed over the whole country, and is to be found in considerable thickness even on hills over r.coo feet high. We have also vast tracts of peat-bog, which not only spread over large areas of low ground, but also extend over the highest hill-tops in thick coatings. Lastly, we have many examples of raised beaches, sea caves, sea stacks, and old river terraces at Kilroot, Lame, Glenariff, Cushendall, and elsewhere round the coast, the river terraces being particularly well marked in the Carey River valley, east of Ballycastle. The accompanying map (Plate Vl.), on a scale of four miles to an inch, reduced from the Geological Survey Map, will serve as a general guide to the formations. METAMORPHIC ROCKS. These rocks are confined, as before-mentioned, to the north east portion of the county. They consist of coarse and fine grained felspathic and quartzose pebbly schistose grits, green chloritic, and grey micaceous schists with bands of quartzose schist, and grey crystalline limestones. Associated with these rocks are dark green epidiorites, and grey and pinkish granulites, which were evidently intruded as igneous veins and large masses previous to the metamorphism of the sediments by earth move ments and crushing. The epidiorites are in great abundance at Torr Head, where they are tangled and sheared up with the crystalline limestones in every conceivable manner. Fine sections are to be seen under the coastguard watch-house. Just north of Cushendun these hornblendic schists (epidio rites) occur also in force, exhibiting beautiful banding and foliation, along with the sedimentary schist rocks into which they have been intruded. Grey and pink banded and foliated felspathic granulites are also very abundant in the schists. In the neighbourhood of Cushendun good sections of them can be seen at several places along the mail-car road to Ballycastle, and close to the old road leading to Torr Head. An intrusive red microgranite mass occurs in the schists to the north-west of Cushendun, smaller bosses, dykes, and veins of the same rock being very common between the main granitic mass and Torr Head. At many places along the public road the relations of these rocks can be readily seen and studied, as well as on the sea-cliff sections between Cushendun and Mur lough Bay. Staurolite and tourmaline occur in the schists close to the main road, about half-way between Cushendall and Ballycastle; also in the vicinity of Ballycastle on the north slope of Knocklayd Mountain. Vein quartz is abundant throughout, especially in Glenshesk THE GEOLOGY 01' CO. ANTRIM. 131 Valley, south-east of Ballycastle, where a thin vein of jade was also found. ORDOVICIAN AND SILURIAN ROCKS. As previously mentioned, these rocks do not occur in the county, but good sections of them are laid open to view along the south shore of Belfast Lough, and generally on the coast of County Down. They consist of greenish and grey grits and occasional conglomerates, with olive, grey, and black shales and slates, the black shales containing graptolites in abundance, especially at Coal Pit Bay, a little south of Donaghadee, where types of both Ordovician and Silurian systems have been found. LOWER OLD RED SANDSTONE. Between Cushendall and Cushendun a considerable thickness of this formation occurs, resting with a strong unconformability A.Iv.'J'-//.-=----~ FiG. I.-FAIR HEAD AND CARRICK :.\lORE LANJJING-STAGE, LOOKING EAST. CARllONIFEROU~ ROCKS AND COLUMNAR INTRUSIVE DOLERITE.-A. ildcHenry. on the Metamorphic rocks. It consists of massive red and brown pebble conglomerates and sandstones, with occasional lenticular red and brown shaly beds. The basal portion, which is on its western margin, is mainly composed of well rounded boulders and pebbles of quartzite, of all sizes from that of a pea to over a foot in diameter. Occasionally pebbles and blocks of porphyry occur, as well as mica-schist fragments. As we ascend in the series, fragments of igneous rocks (felspathic) become more fre quent, while in the uppermost beds, which are on the sea-shore at Cushendall, the rock is almost exclusively composed of angular and sub-angular boulders and detritus of the quartz porphyry that is found in mass on the south, hetween Red Bay and Cushendall.