664 LOUIS AGASSIZ, 



the problem which thej present. This sys- 

 tem reproduces the lines followed by the 

 water over the surface of the ground mo- 

 raines, which covered the whole continent, 

 when the great sheet of ice which modeled 

 the drift broke up and melted away. This 

 conclusion will, no doubt, be as slow of ac- 

 ceptance as was the theory of the ancient ex- 

 tension of glaciers. But that does not trouble 

 me. For my own part I am confident of its 

 truth, and after having seen the idea of a gla- 

 cial epoch finally adopted by all except those 

 who are interested in opposing it on account 

 of certain old and artificial theories, I can 

 wait a Httle till the changes which succeeded 

 that epoch are also understood. I have ob- 

 tained direct proof that the prairies of the 

 West rest upon polished rock. It has hap- 

 pened in the course of recent building on the 

 prairie, that the native rock has been laid 

 bare here and there, and this rock is as dis- 

 tinctly furrowed by the action of the glacier 

 and by its engraving process, as the Handeck, 

 or the slopes of the Jura. I have seen mag- 

 nificent slabs in Nebraska in the basin of the 

 river Platte. Do not the physicists begin to 

 think of explaining to us the probable cause 

 of changes so remarkable and so well estab- 



