Clare Island Survey — Geology. 7 11 



and serpentine boulders which must have come from the east. This 

 lower boulder-clay, forming the main mass of the drift, is overlain by an 

 upper or newer boulder-clay of a brown iron-rust colour, containing grey 

 granite erratics from Corvockbrack, but not containing limestone. The 

 material of the latter drift is much coarser than that of the former, and 

 consists largely of sandstone rock detritus. A similar description applies to 

 an 80-foot section of drift on the shore of the bay west of Carrowmore. This 

 cliff also exhibits along most of its length, especially on its eastern side, a 

 marked difference in colour and composition between the materials of its upper 

 and lower layers, and it is interesting to note that half-way up the cliff there 

 occurs a 10-foot band of stratified sand aud gravel, which at the western end 

 of the cliff dips almost to sea-level. At this end, too, the deposit is particu- 

 larly rich in granite boulders from Corvockbrack. A 40-foot cliff-section of 

 drift at Eoonah Quay, four miles west of Louisburgh, is similarly suggestive 

 of an upper and lower boulder-clay. The 80-foot section on the shore at Old 

 Head, on the other hand, does not show the same distribution of material as 

 is found in the cliff-sections already described, although it also is probably 

 made up of debris contributed by both glaciers. The basal portion of the 

 deposit contains scratched limestone boulders as before, and here the matrix 

 is finely laminated in places, as frequently happens in the lower boulder-clay 

 formation, but serpentine boulders are very prevalent and fairly uniformly 

 distributed throughout the entire section. Here the limestone, as in the other 

 cases, must have come from the east, but much of the serpeutine must have 

 come in the southern ice from the serpentine band running parallel to the 

 shore north of Kilgeever Hill. Owing to the relative geographical positions 

 of Old Head and Corvockbrack, granite boulders from the latter mass coming 

 in the southern glacier would not touch the shore of Clew Bay as far east as 

 the former locality, and consequently no grey granite erratics are to be 

 found in the drift of the Old Head section. 



" The islands in the east of Clew Bay, which consist of drumlin 

 mounds with their western ends deeply cut into by the sea, present 

 excellent sections for the study of the drift of this neighbourhood. In 

 the great cliff of the island of Dorinish More (Plate III, fig. 1), which 

 shows a magnificent section of boulder-clay about 100 feet in height, 

 no essential difference can be noticed between the top boulder-clay and 

 that lower down. The erratics seen in this section are principally scratched 

 limestones with a small proportion of boulders of grit, red granite, schist, 

 etc. At Dorinish Beg a 60-foot cliff-section of boulder-clay is to be seen 

 with the same uniformity of material throughout, except that three or 

 four feet of the deposit at the surface appear to have weathered to a lighter 



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