PROCEEDINGS OF THE OHIO ACADEMY OF SCIENCE. 403 



their a priori speculations concerning the rate of glacial move- 

 ments is a serious blot upon their scientific reputation. 



Coming into the field where more definite evidence of the 

 date of the close of the Glacial period is found, we note that 

 here too there is the same tendency to make exaggerated esti- 

 mates in defiance of the plainest facts of observation. Instead 

 of its being the case that these points to the close of the Glacial 

 period as 30,000 years distant as Penck and a number of our 

 own geologists would place it, and even to a far more distant 

 period as some would recklessly do, there is any amount of 

 cumulative evidence showing that the Glacial period did not close 

 in Europe and America until about 7,000 years ago. The post- 

 glacial gorge below Niagara Falls would be worn by the forces 

 now in operation in 7.500 years. The post-glacial gorge of the 

 Mississippi River below the falls of St. Anthony would have 

 been worn by the forces in operation before the utilization of 

 the falls for manufacturing purposes, in the same length of time. 

 The post-glacial erosion of the various streams in northern 

 Ohio flowing into Lake Erie could easily have been accomplished 

 by the forces now in operation in ten or twelve thousand years. 

 The accumulation of sediment in the glacial lakes that bordered 

 the ice front in northern Ohio show that they did not continue 

 for more than two or three thousand years before the erosion 

 of the Niagara gorge began. The accumulation of dunes south 

 of Lake Michigan and the erosion from the west shore of Lake 

 Michigan set a similar limit to post-glacial time ; while the 

 smallness of the deltas which accumulated in Lake Agassiz at 

 the mouths of such rivers as the Saskatchewan and Assiniboin 

 show that the recession of the ice from the Canadian border to 

 Hudson Bay could not have occupied more than 1000, or at 

 most, 2000 years indicating an average retreat of the ice front 

 of one-half, or at least one-quarter, of a mile a year. Confirma- 

 tory of these calculations is the testimony of Gilbert, Russell, 

 Bell, and others concerning the extreme freshness of glacial 

 striae on the exposed surfaces of rocks in Canada, Utah, and 

 Nevada, showing the absurdity of the extravagant claims so 

 generally made for the antiquity, of the glacial period. 



