i iS The Irish Naturalist. 



level, and where the sections are best exposed, reminded me 

 very much of the sands and gravels of Gloppa, near Oswestry, 

 which occur noo feet above the sea-level. There is little 

 doubt that at one time the whole of the present sea-cliffs of 

 the Hill of Howth were buried in drift, which has been cut 

 away by the action of the sea, leaving the drift in many places 

 merely hanging onto a steep surface of Cambrian rocks at the 

 top of the cliffs. Bailey lighthouse is built upon a spur or 

 promontory of drift based on Cambrian cliffs. 



Let us now cross over Dublin Bay, and examine the splendid 

 sections of sands, gravels, and boulder clay exposed in the 

 cliffs of Killiney Bay. Here we may see and study a typical 

 section of glacial-marine drift, and observe the curious way 

 in which the several beds of sand, gravel, sand and gravel, 

 gravel and boulders, and boulder clay, behave towards each 

 other. In one place we see arched, in another horizontal 

 stratification, elsewhere contorted bands occur, truncation of 

 beds, lamination, and oblique bedding. Indeed, nothing but 

 a careful section can give one any adequate conception of the 

 nature of this drift. Marine shells, or shell-fragments, occur 

 in all of these beds, excepting the horizontally bedded fine 

 gravels near Ballybrack Station. We did not make any 

 attempt to get a complete collection of shells, which would 

 have taken a much longer time than was at our disposal, 

 being principally occupied with drawing the section. We did, 

 however, pick up As f arte arctica, A. sulcata, Cardium edule, 

 My a tru?icata, Tellina balthica, and other indeterminable frag- 

 ments. These are among the commonest shells in glacial 

 deposits. 1 This character of drift continues south along the 

 coast, as far as the River Bray ; but on nearing that river it is 

 underlain by a hard, brown clay, which I call basement clay, 

 with a pretty decided line of demarcation between them. The 

 drift gravels, so far as described, consist, to the largest extent, 

 of Carboniferous limestone, occurring as gravel, pebbles, and 

 boulders — mixed with granite and Cambrian schists, and 

 some flints, chert, &c. The basement clay, though contain- 

 ing these rocks, is much more largely made up of Cambrian 

 schists, slates, and quartzites. These boulders can be seen 



1 Mr. Lloyd Praeger, in the present volume of this Journal, pp. 17, iS, 

 gives a careful provisional list of the shells of the Killiney drift, naming 

 the beds from which they are taken. 



