LAKES EVACUATING THEIR OWN WATERS. 



formed by the deposits of some gigantic lagoon : the 

 tendency would be, as we have shown, for this mighty 

 sheet of water gradually to evacuate itself, by its 

 overflow cutting through whatever it was that ob- 

 structed its outfall. It can be, we think, very conclusively 

 shown that such is the actual tendency of every other 

 existing lake, and the margins of most of the extensive 

 inland sheets of water generally show evident traces 

 of their own levels having been lowered, in this 

 manner, throughout the course of time. The process 

 of cutting through obstructions must however, in all 

 cases be a very gradual one; and of course its effect 

 would be to lower the level of the lake by degrees, 

 as the operation proceeded, until the waters in the 

 end became evacuated altogether, leaving the bed of the 

 ancient lake, laid out by the retreating waters in long 

 and very gradual slopes, very much as we now see 

 it upon the plain of Northern India. 



Opinions of course may differ as to how the mighty 

 work of levelling off the surface of this great plain 

 was effected. It looks, as we have said, as if it had 

 been the sea. But that is merely because people find 

 it perhaps harder to believe in the existence of so 

 great a lake ; but the fact to which attention has already 

 been called, that no marine remains appear in the 

 surface strata, but only those of terrestrial origin, is 

 very significant. These facts are not only conclusively 

 shown by the examination of the surface deposits 

 themselves, when they have been laid open, in ravines, 

 etc., but also by artificial borings penetrating to a 

 considerable depth beneath. We may quote instances 

 of this in a well sunk 48 1 feet deep at Fort William, 

 Calcutta, during the years 1834 to 1840, which passed 



