Notes on Glacial Deposits in Ireland, 163 



scratched, but usually very irregularly. This deposit appears 

 to correspond to those beds on the shore which we have 

 described under the name of " contorted drift," but which, after 

 further study, we now propose to refer to under the general term 

 of " boulder gravels." In the present section, as elsewhere, the 

 boulder gravels rest on red boulder clay, containing numerous 

 fragments of marine shells, and in all respects similar to the 

 boulder clay on the shore. A little further on, behind some 

 cottages, the boulder clay is seen better ; it contains seams of 

 fine red sand free from stones, though in its mass sub-angular 

 and rounded stones of quartzite, Lambay porphyry, Ordovician 

 schist, and L,einster granite are dispersed. Shell-fragments 

 are not uncommon ; Tellina balthica occurs, and pieces of an 

 exotic Pecten. 



A good section of the boulder gravels occurs near a cottage 

 before reaching Vallombrosa. Here a massive deposit, twenty 

 feet in thickness, is seen resting on boulder clay, of which 

 some twelve feet is visible. The boulder gravels are cemented 

 together by carbonate of lime, and stand out in a bold cliff 

 over the road. A little further on, behind a cottage on a bye- 

 road, another section is seen, consisting of some twenty feet of 

 coarse, clean gravel. A census of the boulders and pebbles of the 

 deposit gave 50 per cent. Carboniferous limestone, 30 per cent. 

 Cambrian quartzite, 10 per cent, granite ; and there were also 

 present basalt, L,ambay porphyry, Ordovician ash, flint, slate, 

 and rhyolite, which was identified as coming from Forkill, Co. 

 Armagh. Shell-fragments were found sparingly ; Cyprina 

 isla?idica was the only species recognisable. The deposit rests 

 on boulder clay, and a big granite boulder was observed at the 

 junction of the beds. Such boulders commonly occur in such 

 a position. . 



Following the main road, we now cross the Bray River, and 

 proceed up the southern bank. Opposite where the Vartry 

 water-main crosses the stream, we see a small exposure of blue 

 boulder clay, containing numerous shells, many of them in a 

 nearly perfect state ; Cardium cdule, Tellina Balthica, and 

 Turritella terebra are common, and there were also observed 

 Astarte borealis, Cardhim echi?iattim, and fragments of a Mytilus 

 and a Mactra, and of several indeterminable species. It is 

 worthy of note that the boulder clay at this point is dark blue, 

 whereas almost everywhere else in the Bray valley it is dark 



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