220 On tin Surfaa Geology of th\ Basin of the 



responding to the wide-spread Drift deposits of the north. We 

 there find, however, proofs of erosion on a stupendous scale, 

 such as the valley of Easl Tennessee, which has been formed 

 by the washing out of all the broken strata between the ridges 

 of the AJleghanies and the massive tallies of the Cumberland 

 Mountains, — the canons of the Tennessee, 1,600 feet deep, &c. 

 Here also, as in the lake basin, the channels of excavation 

 pass far below the deep and quiet waters of the lower rivers; 

 proving by their depth that, they must have been cut when 

 the fall of these rivers was much greater than now. 



The history which 1 derive from the facts cited above is 

 briefly this : 



1st. — That in a period probably synchronous with the glacial 

 epoch of Europe, — at least corresponding to it in the sequence 

 of events, — the northern half of the continent of North Ameri- 

 ca had a climate comparable with that of Greenland ; so cold, 

 that wherever there was a copious precipitation of moisture 

 from oceanic evaporation, that moisture was congealed and 

 formed glaciers which flowed by various routes toward the 

 sea. 



2ud. — That the courses of these ancient glaciers correspond- 

 ed in a general way with the present channels of drainage. The 

 direction of the glacial furrows proves thai one of these ice rivers 

 flowed from Lake Huron, along a channel now tilled with drift, 



and known to he at least 1 50 feet deep, into Lake Erie, which was 

 then not a lake, but an excavated valley into which the Streams of 



Northern Ohio flowed, LOO feet or more below the present lake 

 level, following the line of the major axis of Lake Erie to near 

 astern extremity, here turning north-east, this glacier passed 

 through some channel on the Canadian side, qow tilled up, into 

 Lake< mtario, and thence found its way to the sea either by the 



St. Lawrence or by the Mohawk and Hudson. Another glacier 



occupied the bed of Lake Michigan, having an outlet southward 

 through a channel — now concealed by the heavy beds of drift 

 which OCCUpy the Bnrface about the south end of the lake — 



