64 MAX AND THE GLACIAL PERIOD. 



enough to facilitate the movement across it of floating 

 ice, would render it impossible for the ice to have loaded 

 itself with them. 



The same line of reasoning is conclusive respecting the 

 innumerable boulders which cover the northern portion 

 of Ohio, where I have my residence. The whole State of 

 Ohio, and indeed almost the entire Mississippi basin be- 

 tween the Appalachian and the Eocky Mountains, is com- 

 pletely covered, and to a great depth, with stratified rocks 

 which have been but slightly disturbed in the elevation of 

 the continent ; yet, down to an irregular border-line run- 

 ning east and west, granitic boulders everywhere occur in 

 great numbers. In the locality spoken of in northern 

 Ohio the elevation of the country is from two hundred to 

 five hundred feet above the level of Lake Erie. The near- 

 est outcrops of granitic rock occur about four hundred miles 

 to the north, in Canada. After the meeting of the Ameri- 

 can Association for the Advancement of Science in To- 

 ronto in the summer of 1889, I had the privilege of join- 

 ing a company of geologists in an excursion, conducted 

 by members of the Canadian Survey, to visit the region 

 beyond Lake Mpissing, north of Lake Huron, where the 

 ancient Laurentian and Huronian rocks are most typically 

 developed. I took advantage of the trip to collect speci- 

 mens of a great variety of the granites and gneisses and 

 metamorphic schists and trap-rock of the region. On 

 bringing them home I turned them over to the professor 

 of geology, who at once set his class at work to see if they 

 could match my fragments from Canada with correspond- 

 ing fragments from the boulders of the vicinity. To the 

 great gratification, both of the pupils and myself, they 

 were able to do so in almost every case ; and so they might 

 have done in any county or townshij) to the south until 

 reaching the limit of glacier action which I had previously 

 mapped. Here, at Oberlin, on the north side of the water- 

 shed, it is possible to imagine that we are on the southern 



