18 WALKS AND TALKS. 



Simeoe. In Michigan, the nearest source is north of Lake 

 Ilunm ami south of Lake Superior. So in Indiana, Illinois, 

 and the north-west generally, we must go northward to find 

 rocks in place which are of the same sorts as the bowlders. 

 This is plainly demonstrated in the case of bowlders of native 

 copper, which are frequently found in Wisconsin, Illinois, 

 Indiana, Michigan, and Ohio. There is no other credible 

 source than the native copper region south of Lake Superior. 

 So, in the case of the Pierre a bot, near Neufchatel, the 

 nearest credible source is the Mont Blanc chain of Alps, sev- 

 enty miles distant, and separated by the valley of Switzerland 

 and the Lake of Geneva. 



We seem authorized to conclude, therefore, that the 

 bowlders have been transported generally from the north ; 

 that many of them have been moved one or two hundred 

 miles; that they have sometimes been borne over regions 

 which are now lake-basins; that they have been carried, at 

 times, to higher levels than their origin, and much higher 

 than valleys over which they passed ; that a vast mass of sand, 

 gravel, and clay was moved with them, since they lie imbed- 

 ded in these accumulations, to the depth, sometimes, of one 

 or two hundred feet. 



These conclusions will be borne in mind when we come to 

 seek for the nature of that tremendous agency which could 

 have performed so vast a work over all the northern half of 

 at least two continents. (Talks IV and XL VII.) 



III. THE GRAVEL F>rr. 



ARRANGEMENT OP THE DRIFT. 



SHALL we proceed? This subject has its. alphabet, like 

 most others; and every child can testify that there is little 

 inspiration in the alphabet. A few more letters of our alpha- 

 bet will be found in the arrangement of the loose materials 

 which cover the surface of the northern states. These ma- 

 terials are called Drift. The bowlders are a part of the Drift. 



