No. 4.] CLAYPOLE — PRE-GLACIAL GEOGRAPHY. 201 



Champagne county, beyond which it has not been traced. Its 

 western margin is sharply marked at Chatsworth in Livingstone 

 county, where it has a depth of 200 feet, and reaches the Cin- 

 cinnati group. Farther north, its boundary walls are composed 

 of Niagara limestone, and terminate in buried cliffs on the Calu- 

 met and Kankakee Rivers. At Bloomington this trough has a 

 depth of 230 feet. . . . Where penetrated in other localities 

 the depth of this channel is from 75 to 200 feet." 



This channel leaves the basin of Lake Michigan near Chicago, 

 where the land is now but few feet above the level of the lake, 

 and its course appears to be marked out by a remarkable chain 

 of forest oases in the prairies of Illinois, extending along the 

 line indicated above. Whether, however, it reached the Missis- 

 sippi directly, or indirectly through the valleys of the Wabash 

 and Ohio, is not easy at present to determine. Further investi- 

 gation along the line of the buried channel, can alone set at rest 

 this uncertainty. 



The depth of Lake Michigan may be set down at about 900 feet, 

 and if we assume this and the greatest known depth of the buried 

 channel at Bloomington as data, we find that, with the rate of 

 elevation previously employed, the bed of the lake was 170 feet 

 above the bottom of the buried channel. Here therefore we 

 have an outlet by which the waters of the Michigan valley escaped 

 into the great midland plain, and reached its draining stream, 

 the Mississippi. In that event there was a river which may be 

 named for the present the pre-glacial Michigan, traversing the 

 long vale of the same name, narrower and deeper than those 

 before described, and yet with sides sloping only about twenty- 

 five feet in a mile. 



Reviewing the results thus obtained, the early Quaternary 

 Geography of the North American continent presents to the eye 

 an appearance very different from that of the present day. The 

 great river of the north-east was not the St. Lawrence but the 

 Mohawk. Rising in the slopes of the wide and open Huron 

 valley, it passed thence through the gorge at Detroit into the 

 vale of Erie receiving tributaries on both banks. Thence it 

 found its way through a similar gorge not very far from Niagara 

 into the Ontarian valley, receiving on its way the waters of the 

 Genessee, the Ottonnabee, and perhaps also of the Ottawa. It 

 passed onwards through the deep and drift-filled channel under 

 Lake Onondaga and the valley of the present Mohawk to the 



