GEOLOGY. 253 



the streams were excavated to a far greater depth than they are at 

 present. This is proven by the explorations which have been made 

 in all the country bordering Lake Erie in search of rock oil. The 

 borings made upon the Upper Ohio and its tributaries, as well as 

 along the rivers emptying into Lake Erie, show that all these streams 

 flow above their ancient beds, the Mahoning and Shenango, at their 

 junction, one hundred and fifty feet ; the Cuyahoga, at its mouth, 

 over one hundred feet above the bottom of their rocky troughs. The 

 valley of the Mississippi at St. Louis and Dubuque, and the Missouri 

 at and above Council Bluffs, exhibit precisely similar phenomena, 

 deep troughs excavated in the rock by the ancient representative 

 of the present streams, subsequently submerged and filled up with 

 drift clay, gravel, or loess ; these troughs having been but partially 

 cleared of these accumulations by the action of the rivers during what 

 we call the present epoch. 



(7) Along the margins of the great lakes are distinct lines of 

 ancient beaches, which show that in comparatively recent times the 

 water level in these lakes was full one hundred feet higher than at 

 present. 



The facts enumerated above seem to justify us in the following in- 

 ferences in regard to the former history of this portion of our conti- 

 nent. (A) At a period corresponding with, if not in time, at least 

 in the chain of events, the glacial epoch of the Old World, the lake 

 region, in common with all the northern portion of the American conti- 

 nent, was raised several thousand feet above the level of the sea. In 

 this period the fiords of the Atlantic (and probably Pacific) coasts 

 were excavated, as also the deep channels of drainage which, far 

 above their bottoms, are traversed by the Mississippi and its branches, 

 and indeed most of the streams of the lake country. 



During this period Lake Erie did not exist as a lake, but as a val- 

 ley, traversed by a river to which the Cuyahoga, Vermillion, Chagrin, 

 etc., were tributaries. In this " glacial epoch " all the lake country 

 was covered with ice, by which the rocky surface was planed down 

 and furrowed, and left precisely in the condition of that beneath the 

 modern moving glaciers in mountain valleys. Could we examine the 

 surfaces upon which rest the enormous sheets of ice which cover so 

 much of the extreme arctic lands, we should doubtless find them ex- 

 hibiting the same appearance. 



(B) At the close of the glacial epoch all the basin of the great lakes 

 was submerged beneath fresh water, which formed a vast inland sea. 



From the waters of this sea were precipitated the laminated clays, 

 the oldest of our drift deposits, containing trunks and branches of 

 coniferous trees, a few fresh-water and land shells, but no oceanic fos- 

 sils. Parallel beds on the St. Lawrence generally contain marine re- 

 mains. It would seem, then, that this was a period of general sub- 

 sidence throughout the northern portion of our continent, and that 

 the Atlantic then covered a large part of New England and Canada 

 East. 



(c) Subsequent to the deposit of the blue clays, an immense quantity 

 of gravel and boulders was transported from the region north of the 

 great lakes, and scattered over a wide area south of them. 



That these materials were never carried by currents of water is 



99 



