Ancient Drainage ofJVorth America, Sfc. 17 



into the Mississippi. The south-east slope of this table land, 

 furnishes the great eastern line of drainage of this continent. 

 At some remote geological period, it is evident all the parts of 

 this basin have been under water, which has subsequently re- 

 treated to the ocean ; leaving behind those subordinate basins 

 or inland seas now called lake Superior, lake Michigan, lake 

 Huron, lake Erie, and lake Ontario, which are the true heads of 

 the line of drainage by the St. Lawrence. Lake Superior is 

 595 feet above tide water. Lakes Michigan and Huron, which 

 constitute one body of water, are 571 feet above tide water; 

 whilst lake Erie is 565 feet, and lake Ontario only 231 feet. 

 Thus whilst in the distance between Rainy lake, and lake Su- 

 perior, consisting of 150 miles, we have a superficial depression 

 of 505 feet, in the short distance of 25 miles between lake Erie 

 and lake Ontario, we have a depression of 334 feet. 



West of this depression, the conformity of level is such, that 

 part of the waters of the great eastern line of drainage before 

 spoken of, pass, in the rainy seasons, from their proper line, into 

 the tributaries that feed the Mississippi. Boats have occasionally 

 passed from South Michigan into the Illinois river : the differ- 

 ence of level between lake Huron and lake Erie may be rated 

 as not exceeding 10 feet. 



Such are the principal lines of drainage of this continent, all 

 of which are well illustrated in Mr. Tanner's recent maps. But 

 we are yet in want of many levels and projections of chains of 

 mountains, to assist us in detecting the various basins where the 

 waters have been held up, and the slopes and gorges by which 

 they have issued. The immense boulders of primitive rocks, so 

 profusely scattered over the face of this continent, attest alike 

 the partial destruction of their ancient barriers, and the violence 

 of the torrents which have borne them to such great distances. 

 There is not one of the inland lakes, all of which may be con- 

 sidered as subordinate basins to the great American basin before 

 spoken of, but furnishes the proof of a gradual subsidence of 

 level. The ridges south of lake Erie, and from which the lake 

 is now distant more than five miles, clearly attest that the lake 

 at some period has washed their base, and discharged its waters 

 into the tributaries of the Mississippi. In like manner we find 

 evidences of a change of level in the waters of lake Ontario, in 

 Ihc existence of the ridge on the south shore, now several miles 

 Vol. I.— 3. 



