236 THE ICE AGE IX NORTH AMERICA. 



limit to the size of the fragments of rock which can be 

 transported upon the back of a glacier. Nor wo aid there 

 seem to be any definable limit to the distance through which 

 these masses of rock can thus be carried, except as there is a 

 limit to the movement of the ice itself. In walking out on 

 the smooth surface of the eastern part of the Muir Glacier, 

 it was not uncommon to encounter, miles away from any 

 mountains, cubical blocks of stone as much as twenty feet 

 in their several dimensions, which, with countless others of 

 smaller size, united to form a medial moraine. Slowly but 

 surely these great bowlders have been brought to their pres- 

 ent position, and slowly but as surely they are moving on to 

 the front of the glacier, where, in due time, they will be 

 deposited in the terminal moraine. 



Fig. 72.— Vessel Rock, a glacial bowlder in Gilsum, N. H. (C. H. Hitchcock.) 



The summary of facts published by President Hitch- 

 cock many years ago may fitly serve as an introduction to 

 the more detailed account to follow. In this, after remark- 

 ing upon the great size of single bowlders, he illustrates the 

 remark by the following examples : 



The block called Pierre a Bot, near Neufchatel, contains 

 40,000 cubic feet. It has been transported from near Mar- 

 tigny, more than sixty miles, across the great valley of Switz- 



