DRIFT DEPOSITS OF ILLINOIS. 21 



found. This is precisely what we might anticipate if they were 

 trail sported by floating ice, whereas if their occurrence was due 

 to the southward movement of land ice, they should be equally 

 or more abundant at the southern extremity of the ice sheet 

 than elsewhere. 



Dr. Drake, of Cincinnati, in an essay published in the Trans- 

 actions of the American Philosophical Society, in 1825, ad- 

 vanced the theory ' ; that the boulders of foreign material in 

 Ohio, with the clavs in which thev were imbedded, were brought 



/ / 



from the north by floating ice during a period of submergence:" 

 and Sir Charles Lyell, on his first visit to America, adopted a 

 similar view, and explained the drift phenomena observed by 

 him in Canada, as the probable result of floating ice, loaded 

 with the rocks and detritus of the north. 



Prof. Dawson, of McGill College, in his Acadian Geology, ad- 

 vocates a similar theory in explanation of the drift phenomena 

 observed by him in Nova Scotia. In discussing the probable 

 origin of the drift, on page 64 of the volume above cited, the 

 author says: "Let us suppose then, the surface of the laud, 

 while its projecting rocks were still uncovered by surface de- 

 posits, exposed for many successive centuries to the action of 

 alternate frosts and thaws, the whole of the untraveled drift 

 might have been accumulated on its surface. Let it then be 

 submerged until its hill-tops should become islands, or reefs of 

 rocks, in a sea loaded in winter and spring with drift ice, floated 

 along by currents which, like the present Arctic current, would 

 set from X. E. to S. W., with various modifications, produced 

 by local causes. We have in these causes ample means for ac- 

 counting for the whole of the appearances, including the trav- 

 eled blocks, and the scratched and polished surfaces." 



The enormous transporting power of floating ice is well known 

 to be fully adequate to explain the occurrences of boulders, and 

 any other foreign material occurring in the drift deposits, and 

 the low temperature prevailing in the high northern latitudes, 

 from which the foreign material in the drift, of the Mississippi 

 valley has come, furnishes the essential conditions for the break- 

 ing up of solid rocks, reducing the broken masses to the condi- 

 tion of boulders, and transporting and distributing them as far 

 as the drift deposits extend. 



