148 THE VALLEYS OF SOME OF THE IRISH LAKES. 



sometimes being covered by boulder-clay or esker- 

 drift, at other times by a meteoric accumulation 

 formed of the insoluble portion of the limestones 

 that has weathered away. If a swallow-hole forms 

 in a low place, the river during floods will overflow, 

 and form a lake locally called a " blind lough " or 

 turlough. These usually exist in wet weather only, 

 but totally disappear afterward, leaving in their 

 place a rich meadow or pasture. Of one of the 

 turloughs in the County Galway there is a tradi- 

 tion that it was formed by artificial means, a well 

 having been sunk that tapped a river and flooded 

 the hollow, occupying it ever since. In Galway and 

 Clare extensive areas and lakes are drained through 

 subterranean rivers, the outlets from some being 

 unknown. 1 This occurs in other places also in 

 Ireland ; while it appears probable that in ancient 

 times, when the land was much higher than at 

 present, some lakes which now have surface outlets 

 previously had subterranean ones. A description of 

 one of these river systems, devoid of an open outlet 

 to the sea, may be given. 



Lough Cooter receives the drainage of the N.W. 

 shoulder of Slieve Aughta. The Beagh river leaves 

 the north end of Lough Cooter, and flows for about 

 two miles towards the west, when it disappears in a 



1 "Memoirs of the Geological Survey," Exs. and Maps, sheets 115, 

 116, 124, &c. 



