492 G. H. Kinahan — Water Basiii of Lough Berg. 



below the present surface of the water. Such a- passage would be 

 able to drain all the upper part of the lake basin, except four small 

 deeps : one northward of Illaunmore, one immediately west of that 

 island, and two to the S.S.W. of it; but it would be incapable 

 of draining a portion of the long east and west reach and a long 

 narrow tract in the south-west arm of the lake, they being over 

 sixty feet in depth, while in places they are over 100 feet; one 

 spot which is situated in the former, a little on the north-east of 

 Parker's Point, being 119 feet deep. 



In the paper on " Soundings in the Lake of Como," referred to in 

 the introduction, Mr. Ball has pointed out as to a lake basin, " sup- 

 posing the rocks on either side to be of equal hardness, and similarly 

 'stratified, it is safe to afi&rm 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 

 glacier stream was turned aside from its previous direction." Mr. 

 Ball has shown that this 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. 

 If, however, the rocks were broken up in lines by breaks and faults, 

 ice would act along such lines and lift up and carry away rocks, 

 excavating some places, where the rocks were broken, much more 

 deeply than either marine action or ordinary meteoric abrasion 

 could do.^ Such deeps would be nearest to the convex sides of the 

 bends, as the natural action of the ice would excavate away the 

 higher rocks in the section more toward the concave than toward the 

 convex side. 



Ice, however, could scarcely excavate or gouge out the sudden 

 deep holes that occur in so many lake-basins ; to which I would 

 add, that after carefully contouring and examining the Charts of the 

 lakes and bays mentioned in the introduction, I am convinced that the 

 sudden deep holes could not have been excavated by the sea, ice, or 

 ordinary meteoric abrasion; but as all of them seem to occur on breaks, 

 or at the junction of two or more dislocations, it appears inevitable 

 that they are due, at least in part, to fissures formed by the contrac- 

 tion and displacement of the rocks ; while subsequently most, if not 

 all of them, may have been connected with subterranean streams, 

 which at different times drained, or helped to drain, the lake-basins. 

 Ice, when it first forms on a countiy, will be more or less full of 

 foreign matter, viz. the broken rocks and other detritus that occur 

 at the surface; after a time, however, all these will be carried away ; 

 so that if the Lough Derg basin had been for ages occupied by ice, 

 most, if not all, of the loose portions would have been removed out of 

 it, leaving the ice, prior to its final disappearance, comparatively 

 speaking, pure, and without any rock detritus in it, to incumber the 

 lake basin ; therefore, none of the deeps in it could have been filled 



^ The Eev. M. H. Close is of opinion that "there never was 'a glacier' in the 

 basin of Lough Derg. That basin, however, was no doubt swept by a flow of the 

 general ice-covering of the country." 



