THE VALLEYS OF SOME OF THE LRISH LAKES. 157 



have been obliterated, and the water forced to find 

 other outlets. This may also have been the case 

 in regard to the basin of Lough Derg, as the valley 

 extending from the long east and west reach through 

 Tough al Bay round the hills called Slieve Arra, and 

 down the valley of the Kilmastulla river to the 

 valley of the Shannon, a few miles south of Killaloe, 

 is occupied by an accumulation of deep drift, prin- 

 cipally gravels and sands, apparently of the " Esker 

 sea " period. This drift may be of any depth, and 

 fill a deep valley ; and if such a valley once existed, 

 meteoric abrasion, or even sea action, would have 

 been capable of excavating out the basin of Lough 

 Derg about 60 feet below the present surface 

 of the waters of the lake, that is, down to a level 

 nearly equal to the height of the barrier of rocks that 

 form the rapids and fall of Doonass in the neighbour- 

 hood of Castleconnel. Such a passage would drain 

 all the upper part of the lake-basin, except four 

 small deeps, one northward of Illaunmore, one im- 

 mediately west of that island, and two to the S.S.W. 

 of it ; but it would be incapable of draining a long 

 narrow tract in the S.W. arm of the lake, also a 

 portion of the east and west reach, they respectively 

 being over 60 feet in depth, and in many places 

 over 100 feet ; the deepest place, which is situated in 

 the latter, and lies a little to the N.B. of Parker's 

 Point, being 119 feet. Mr John Ball, F.R.S., &c., 



