LABORS OF ICE-BORN TORRENTS, ETC. 225 



New York, the growth of the continent was toward the 

 south, the rocks of the Lower Silurian must lie to the north 

 of Niagara Falls, and the rocks of the Devonian to the 

 south. From either of these regions trace a line parallel 

 with the axis of the lake waters — omitting Lake Superior 

 — and we have the geographical boundary of a system of 

 rocks, or one of the shore-lines of the ancient continent. 



It is a curious fact that the great lakes were excavated 

 along the outcrops of the formations instead of across them. 

 It is not an unaccountable fact, for the lines of least resist- 

 ance must have run along the trends of the most friable 

 strata. Lake Michigan is scooped out from Devonian for- 

 mations ; and the same is true of Lake Erie. Lake Ontario 

 is excavated in Lower Silurian strata ; and the same is true 

 of Georgian Bay, Green Bay, and the Wisconsin lakes far- 

 ther south — Winnebago, Horicon, and Albion. The basin 

 of Lake Huron is underlaid by Devonian and Upper Silu- 

 rian rocks. It seems to be two basins coalesced ; and but 

 for the peninsula of Niagara limestone separating it from 

 Georgian Bay, it would be three' basins blended in one. 

 Lake Champlain also conforms to the trend of Lower Silu- 

 rian strata, but the small meridional lakes of Central and 

 Western New York are plowed across the formations. 

 They are a kind of inland fiords, worked out perhaps rather 

 by the action of the glacier than by that of the floods 

 which followed. 



The influence of these vast inland accumulations of fresh 

 water upon the comfort and happiness of man is strikingly 

 beneficent and providential. They serve as equalizers of 

 summer and winter temperatures. In winter they may 

 be regarded as vast reservoirs of warmth — great natural 

 stoves or heaters, which continue to impart their warmth 

 to the frigid winds that move over them, and thus transfer 

 their influence to the contiguous lands. This is a provision 



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