High and Low- level Shelly Drifts around Dublin and Bray. 121 



level of about 860 feet above the sea a very careful search in a 

 large gravel-pit yielded a few glacial shell fragments of the 

 ordinary' type, but indeterminable ; most were chalky and 

 carious. A microscopic examination after riddling disclosed 

 the presence of a few shelly grains as also much granitic debris. 

 There is a great development of drift in this valley which is 

 best seen from the opposite side near the reservoir of the 

 Rathmines Waterworks. It is buff- coloured, clayey, to the 

 greatest extent limestone, but also containing granite, 

 Ordovician grit, and felstone. Some of the limestone pebbles 

 are striated. It is quite remarkable how this limestone gravel 

 has been swept up the valley and rests on the granite forming 

 the bottom rock. The drive back on the opposite side of the 

 valley — after a pleasant lunch in a sunny hayfield and admiring 

 glances at Kippure rising majestically at the head of Glen- 

 nasmole — showed plainly that, though the drift is still in great 

 force, much of it has been removed by denudation. 



We may now with advantage devote a little attention to 

 Glencullen. This valley drains to the south-east, or in the 

 opposite direction to that of the upper part of Glennasmole. 

 In it is to be seen a grand development of drift, which has 

 already been described in this Journal by Professor Grenville 

 Cole, who accompanies his observations with a good photo- 

 graph. 1 This drift is of a very stony nature, so much so that 

 I had to get a specimen I wanted out with a chisel. It is 

 mostly full of Carboniferous limestone pebbles of a dark blue 

 colour ; some well worn, and many well striated — some of the 

 boulders intensely so. There is also a considerable propor- 

 tion of Wicklow granite, some mica schist, and many flakes 

 of mica ; also boulders of red conglomerate from the ^ase of 

 the Carboniferous. The granite increases in proportional 

 quantity as we ascend the glen, until at Glencullen Bridge it 

 becomes predominant. In many places great blocks of gravel 

 are cemented together into a natural concrete by the deposit 

 of carbonate of lime. Further south, below Enniskerry, strati- 

 fied yellow sands are seen on the right bank of the Cookstown 

 River, probably 100 feet thick. In these sands are thin beds 

 of crushed granite and occasional thin beds of limestone 

 gravel. 



(TO BE CONCLUDED). 



1 a 



County Dublin, Past and Present." L N., 1892, p. 92 



