158 THE VALLEYS OF SOME OF THE IRISH LAKES. 



in a paper on " Soundings in the Lake of Como," 

 has pointed out as to a lake-basin, " Supposing the 

 rocks on either side to be of equal hardness and 

 similarly stratified, it is safe to affirm, that if they 

 had been hollowed out by glacial action or by 

 aqueous erosion, the slope would be steepest on the 

 concave side of the bend, in those parts of the lake 

 where the glacial stream was turned aside from its 

 previous direction." This Ball has shown is not 

 the case in the basin of the Lake of Como ; neither 

 is it the case in the Lough Derg basin, as at all 

 such bends the slopes are steepest at the convex side 

 of the bends, while the deepest part of each cross 

 section is nearest to the same side. 



After carefully contouring and examining the 

 charts of three Irish lakes, Loughs Corrib, Mask, 

 and Derg, we have found, in all, sudden deep holes 

 which it seems impossible either the sea, ice, or 

 meteoric abrasion could have excavated; while as 

 they occur on or at the junction or crossing of 

 breaks, we would suggest that they are in part 

 due to the fissures which were formed by the con- 

 traction of the rocks, and that subsequently most, 

 if not all of them, may have been connected with 

 subterranean passages, which at different periods 

 drained or helped to drain the lake-basins. If the 

 Lough Derg basin had been, for ages, occupied by a 



1 Geological Magazine, vol. viii. No. 8, August 1871. 



