ANNUAL OF SCIENTIFIC DISCOVERY. 



certain, as their gravity, especially that of the copper, would bid de- 

 fiance to the transporting power of any current which could be driven 

 across the lake basin ; indeed, that such was not the method by which 

 they were carried is conclusively proved by the fact that, between 

 their places of origin and where they are now found, the blue clay 

 beds previously deposited now lie continuous and undisturbed. By 

 any agent, ice or water, moving over the rocky bottom of the lake 

 basin, carrying with it gravel and boulders, these clay beds would 

 have been entirely broken up and removed. The conclusion is, 

 therefore, inevitable that these immense masses of northern drift 

 were floated to their resting-places. All the facts which have come 

 under my observation seem to me to indicate that, during countless 

 years and centuries, icebergs freighted with stones and gravel were 

 floating from the northern margin of this island sea, melting and 

 scattering their cargoes on or near its southern shores. Subsequently, 

 as its waters were gradually withdrawn, these transported materials, 

 rolled, comminuted, and rearranged by the slowly retreating shore 

 waves, were left as we now find them, heaps and imperfectly stratified 

 beds of sand and gravel. 



(D) In the lake ridges (ancient beaches), 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 depression of 

 the water level was effected. If, with the topography of the basin 

 of the lakes remaining precisely 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 

 togther 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, etc. 

 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 t-he 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 Mississippi 

 Hooded. 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 such 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 



