*t 14 Proceedings of the Royal Irish Academy. 



drift which is obviously later than the lower or limestone boulder-clay. 

 It is clear that these foreign boulders must have reached the island in the 

 District Glacier that came from the south-east. From a little rocky bay 

 south-east of the old abbey, and situated about 600 yards from it, Professor 

 I. Swain obtained a very interesting collection of foreign boulders. These 

 included specimens of calc-diabase, schistose diabase, altered porj)hyritic 

 rhyolite, gneiss, amphibolite, and red granite ; but as it is impossible to trace 

 the rocks to their source, they do not throw any light on the ice-movements 

 under discussion. Various other erratics corresponding in character to local 

 rocks, but often differing lithologically from those that underlie them, are 

 widely distributed over the island, even at the greatest elevations. Amongst 

 others, a large boulder of red sandstone-conglomerate, weighing about a ton, 

 remains perched almost on the summit of Croaghmore. 



Glacial Dkifts. 



Boulder-Clay. 



As the distribution and extent of the various superficial deposits of Clare 

 Island are sufficiently indicated on the accompanying colour-printed map, 

 they need not be referred to here in any great detail. A more exhaustive 

 account of them will be found in the Geological Survey memoir already 

 mentioned. The chief of these deposits is the boulder-clay ; this drift rests 

 on the low rock-platform fringing practically the whole of the north-eastern, 

 eastern, and southern coasts, and extends inland from the sea-margin for 

 various distances up to that of about a statute mile. The form of the ground in 

 the boulder-clay area is hummocky, with the hollows between the drift-knolls 

 often occupied by little flats of peat or alluvium. Great numbers of loose 

 angular boulders lie strewn on the surface of the hummocks, especially in the 

 north-eastern corner of the area ; on the southern coast the surface features 

 of the deposit are smoother in outline, with fewer boulders encumbering the 

 ground. At Eooaunbeg, to the south-east of Knocknaveen, the deposit 

 assumes the form of a longitudinal mound or dtumlin ridge, having its long 

 axis oriented in the direction of the principal ice-movement ; this hummock 

 forms quite a conspicuous feature of the landscape. The best sections of the 

 boulder-clay are seen along the north-eastern coast, where cliffs have been cut 

 in the deposit by the erosive action of the sea. These cliff-sections exceed a 

 vertical height of 40 feet at various points along the coast, while at 

 Leckaprison a vertical section of more than 70 feet of boulder-clay is 

 exposed. 



