Clare Island Survey — Geology. 7 15 



The most cursory examination of the sections reveals the presence of two 

 distinct varieties of the deposit. In the deeper layers the matrix of the till 

 consists of fine-grained dark-grey material, closely compacted, and containing 

 numerous scratched limestone boulders. Besting on this stratum is a much 

 coarser and looser material, which is lighter in colour, and characterized by 

 the absence of limestone blocks. The latter variety of the deposit, however, 

 contains a considerable proportion of angular, or but slightly glaciated, rock- 

 fragments. An analysis of representative samples of these types, made by 

 Mr. P. A. Baldock, of Liverpool University, shows that, the lower or lime- 

 stone variety contains, in its finer material, an average of about 18'5 percent. 

 of carbonate of lime as against Soper cent, of that ingredient in the upper 

 portion of the deposit. In this part of the island, the limestone boulder-clay 

 attains a thickness of from about 12 feet at Leckascannalmore to about 

 25 feet at Ooghmacnamara ; it is completely covered all along this coast by 

 the upper or non-calcareous drift. It is only in the south of the island that 

 the limestone boulder-clay appears at the surface, where it is traceable from 

 the drumlin at Eooaunbeg northwards along the Owennvore stream up to 

 about the 300-foot contour-line. To the south-west of Croaghmore, the drift 

 is extremely coarse and morainic in character, and seems to have been 

 brought thither in the higher part or on the surface of the glacier, and then 

 let down loosely on the rock-floor as the ice melted. 



It may be mentioned here that a remnant of glacial drift still persists on 

 The Bills, which are rocky islets, lying well out to sea, about eight miles to 

 the north-west of Clare Island. 



It is interesting to note that the sandy boulder-clay at Ooghcorragaun, in 

 the north of Clare Island, contains small fragments of marine shells. 

 Mr. J. de W. Hinch, who made this important observation, has kindly 

 furnished the following account of his discovery : — 



Notes on the Glacial Mollusea of Clare Island and North Mayo. 



The only locality on Clare Island in which any shells were found was a 

 stretch of the coast-line around OoghcoiTagaun. Here in the calcareous 

 boulder-clay a considerable number of shell-fragments were found. Most of 

 the fragments obtained were in too poor a condition to be identified, but 

 the following genera and species were recognisable : — 



Lamellibranchiata : — Ostrea edulis Linn., Mytilus sp., Pecten opercular U 

 Linn., Cardmm echinatum Linn., Cardium edule Linn., Saxieava rugosa Linn. 



GASTEROPODA ■.—Patella vuhjata Linn., Tv.rritella communis Bisso, 

 Dentaliuni sp. 



Cirripedia : — Balanus sp. 



