Pi'.'niYi'.KiDr. K Si PuAi'XiKii — Vcijchdion Soil/// of J)til)/iu. 



GKOLOGY AND IMI YSIO(JUA?ir Y. 



The district to which the present paper refers cornpris(^s nn area 

 of some 200 square miles of hmd surface. Its eastern boundary — 

 the only natural one — is fornuMl by tlio wati^rs of tli(5 Irish Sen. 

 On the north it is boundcMl by :i str;u^lit line I'unning some twelves 

 miles, diw westwards, inland from tlie mouth of the liiver Liffey 

 tiloui;- th(^ soutli -eastern vdi^v- of the jjjreat central linu^stonc^ ])lain of 

 the country. Tlie southern boundary is formed by a line running 

 inland from the coast, just south of liray Head, due westwards, for 

 some seventeen miles, to a point (Lilfey Cottaj;(>) ;ibout one mile 

 and a half north-east of the village of Hlessington, tlu; line thus 

 traversing the northern end of the Wicklow Mountains. Tlie 

 western boundary is a line; running du(( north and south, principally 

 along the limestone ])lain, froui iiill'ey Cottag(i to a point bcitween 

 Leixlip and Celbridge, and passing through the village; of JNewcMstlc. 

 A. glance at an ordinary map of this district will show tlierefore that, 

 speaking generally, it consists of a single, broad physiographical 

 contrast between plain on the north and north-west, and mountain on 

 the south. 



This southern ]);trt embraces tlu; nortluu-n end of t\w Leinster 

 granite chain, whicli ext(Mids thence south- w(!stwards for sixty or 

 seventy miles. These granites are of post-Ordovician and ])re- 

 Cai'boniferous age ; and it has Ix^en suggested by Professor Sol las that 

 they were fornuMl as an immense; laccolite, witli an Ordovic-ian cover 

 and a ('ambrian llooi'. It is certain that tin; advtMit of ( 'arboniferous 

 times found denudation already so fui- advanced that the granite; was 

 exi)osed, and the; Cand)rians stri])ped of th(;ir Silurian eov(>i-ing, for 

 rocks of (!arbonif(;rous age an; to be se(;n r(;Hting direcllyon both. 

 The area included in our map, tlien, pr(;scnts in the south a solid 

 nuiss of granite (which rises to 247.'> feet in Kippure), Hanked by 

 Cambrian and Ordovician slates. All dip down under the Carboniferous 

 limestone, which forms a ])lain stretching across the western and 

 northern part of tlie area, and in which stands the city of Dublin. 



No rocks newer than the Lower Carbonif(;rous go to the building 

 up of our area, till one com(;s to tlu; (Uacial deposits. Tliese, 

 however, are thick and extensive, and profoundly affect tlu; distri- 

 bution of the vegetation. An almost continuous sheet of calcareous 

 Boulder-clay, mainly derived from the great plain of Cnrboniferous 

 limestone whicli lies to tlu; west and north, is spicad over the 



