45 



fully described by Col. Whittlesey and others, we have evidence that 

 the water of the lakes remained for considerable intervals much 

 higher than at present. By careful study of these ridges we may 

 hereafter be able to map the outlines of the great inland sea, of which 

 our lakes are now the miniature representatives, and to determine by 

 what causes, whether by local subsidence of some portion of its 

 shores, or the cutting down of channels of drainage, this great de- 

 pression of the water-level was effected. 



If, with the topography of the basin of the lakes remaining pre- 

 cisely what it now is, the water-level were raised one hundred feet, 

 to the ancient beach which runs through the city of Cleveland, the 

 whole of the chain of lakes would be thrown together and form a 

 great inland sea. 



By this sea, a large portion of the State of New York would be 

 submerged, much of Canada lying in the basin of the St. Lawrence, 

 most of the peninsula of Canada West, the greater part of Michigan, 

 and a wide area south and west of the lakes in the States of Ohio, 

 Indiana, Illinois, Wisconsin, &c. 



Indeed, raised to this level, the water of the lakes would submerge 

 deeply the summit between Lake Ontario and the Mohawk, and es- 

 cape at once through the Hudson to the ocean, as well as by the out- 

 let of the St. Lawrence. At the west a similar state of things would 

 exist ; the Kankakee summit, the divide between Lake Michigan and 

 the Mississippi, now scarcely more than twenty feet above the lake 

 level, would be deeply buried, and the whole valley of the MississijDpi 

 flooded. We apparently have proof that the lake waters did once 

 flow over this summit, as it is said that lake shells are found beneatH 

 the soil over nearly all parts of it. 



While it is entirely possible that the low points in the rim of this 

 great basin have been worn down to the present inconsiderable alti- 

 tude by the action of the water flowing from it, and that the former 

 inland sea was drained by the simple process of the wearing down of 

 its outlets, we may well hesitate to accept sucli an explanation of the 

 phenomena until conclusive evidence of its truth shall be obtained. 



Geological history affords us so many examples of the instability of 

 our tejTu Jirma^ that we can readily imagine that local changes of 

 level in tbe land have not only greatly affected the breadth of water- 

 surface in the lake basin, but have perhaps in some instances pro- 

 duced what we have sujjposed to be proofs of great and general ele- 

 vations of the water-level, which are, in fact, only indications of a 

 local rise of the land. 



Nothing short of years of patient observation and study will enable 

 us to write anything like a complete history of the great changes 

 which have taken place in the physical geography of the basin of the 



