Clare Island Survey — Geology. 7 21 



mosses, and the elytra of beetles has been dredged in the North Sea, on the 

 slopes of the Dogger Bank, from a depth of 22 to 23 fathoms. 1 The occurrence 

 of submerged peats and forests round the Irish coast is dealt with fully in 

 the Geological Survey memoir on Clare Island, and in the map (Plate V) 

 prepared for that memoir are shown the localities in which these deposits 

 have been found. As they occur fairly uniformly round the coast, the 

 inference is that the whole island has sunk from the position which it 

 occupied during the peat and forest period. The partially submerged bog at 

 the back of Dunworley Bay, Co. Cork, furnishes us with evidence of a con- 

 siderable subsidence within recent times. This bog, the surface of which at 

 present stands at about the level of high tide, has been bored to a depth of 

 50 feet without reaching the bottom of the peat-deposit. As peat could have 

 accumulated only above high water, we have here evidence that this area 

 must have sunk, at least, more than 50 feet from the level which it occupied 

 when the peat began to form. In Britain, the position of the submarine 

 peats proves a subsidence of the land of at least 60 or 70 feet from its former 

 level; it is, therefore, fairly certain that the whole of the British area 

 participated in the movement to a similar extent. 



Probable Post-Glacial Land Connexion of Clare Island with the 

 Mainland. 



On all the low ground fringing Clew Bay, great accumulations of drift 

 remain as testimony to the vast amount of material that must have 

 been imported by the principal ice-sheet that invaded this region. Along 

 the coast near Louisburgh, and in the islands in the east of the bay, formidable 

 cliffs of boulder-clay, often 100 feet in height, are of frequent occurrence. 

 Great depths of drift occur also on Clare Island itself, and along the northern 

 shore of Clew Bay, so that on the low ground on every side of the present 

 basin, there are found vast deposits of loose glacial material, which 

 undoubtedly extended far seawards in former times. The isobaths or contours 

 made from the soundings in Clew Bay give us a good idea of the form of the 

 sea-floor in this area. A reference to the map (Plate VI) shows that the bay 

 is really a very shallow inlet of the sea. Nowhere in the basin does the 

 depth exceed 20 fathoms, while the shallow strait separating Clare Island 

 from the Louisburgh coast is less than 60 feet in depth. 



1 Clement Reid and (Mrs.) Eleanor M. Keid. " Some Notes on ' Moorlog,' a Peaty Deposit from 

 the Dogger Bank in the North Sea." Essex Naturalist, Part I., vol. xvi (1909), pp. 51-60. 



R.I. A. PKOC, VOL. XXXII. D 7 



