98 



The hish Naturalist. 



April, 



the ice has dammed back the waters into some small lateral 

 valley, forming a temporarj- lake. If there happened to be a 

 col in the range of hills low enough, the waters of the lake 

 would drain over this instead of along the margin of the ice 

 sheet, as in the following illustration ; — 



Diagram to iIvI.ustrate formation of Lateral Lake and 

 consequent drainage over a coi,. 



The Marjelen See in Switzerland affords an instance where 

 drainage of this kind actually occurs during portion of the 

 year, and similar phenomena have been explained in a similar 

 way with great success in many parts of England and America. 



In the case of the general ice sheet melting away, and 

 leaving bare hill=, such as the Dublin Mountains, not 

 high enough to have a local ice-sheet of their own, this 



