7 6 Proceedings of the Royal Irish Academy. 



pyrites, and indeed the entire band is suggestive of a mineral lode. The 

 great variety of rock-types, which include serpentine, dolomite, biotite- 

 lamprophyre, dolerite, olivine-basalt, &c, occurring here, within a compara- 

 tively small area, must he attributed to successive intrusions of igneous 

 material into the zone of fracture. Serpentine and dolomite of the same 

 date as the corresponding rocks just mentioned appear also as a narrow band 

 in the faulted area at Portruekagh. 



The only other igneous rocks in the island are a few masses of epidiorite 

 exposed in the neighbourhood of Kill, some minor basic intrusions in the 

 townlands of Ballytoohy More and Ballytoohy Beg, and a small basic sill, 

 south of Croaghmore, in the townland of Bunnamohaun. 



An explanation of the system of faulting by which the older Ballytoohy 

 strata were brought down against the newer Knoekmore series may be here 

 desirable. Mr. Kilroe accounts for this anomaly by supposing that an 

 upthrust from the north took place early in the history of the district, in 

 fact contemporaneously with the dislocation that produced the inversion of the 

 strata of Croagh Patrick, in post-Wenloek, and probably early Old Bed Sand- 

 stone, times. The older northern series was thus brought to a high level, and 

 when a certain amount of denudation had taken place, and after the Upper 

 Old Bed Sandstone and Lower Carboniferous beds had been deposited on the 

 shores of this old land-surface, normal faulting ensued, bringing down the 

 Carboniferous rocks against the Lower Old Bed Sandstone series, and the 

 older northern series against the newer southern group. 



Glacial and Post-Glacial Geology. 



During the progress of the Biological Survey of Clare Island there arose 

 many problems concerning the present distribution of the fauna and flora of 

 that district, and incidentally of Ireland as a whole, for the solution of which 

 as full a reconstruction as possible of the recent geological history of the 

 island is of fundamental importance. Had Clare Island already been cut off 

 from the mainland in late pre-Glacial times ? Was it overwhelmed with ice 

 in the general glaciation of the Great lee Age \ Was there a land-bridge 

 uniting the island with the mainland on the recession of the ice, or has there 

 been a land-connexion between them at any subsequent date ? What 

 changes in the relative level of the sea and land have taken place over the 

 Irish area during the Pleistocene and Beeent Periods ? AB these are 

 questions deeply concerning the problems which the biologists that took 

 part in the Clare Island Survey have set themselves to solve. 



The present writer, whose privilege it was to examine and map for the 

 Geological Survey of Ireland the superficial deposits of Clare Island, kept 



