CHAP. VII.] 



THE GLACIAL EPOCH. 



105 



that could have produced them. Whenever the Swiss glaciers 

 retreat a little, as they sometimes do, the rocks in the bed of the 

 valley they have passed over are found to be rounded, grooved, 

 and striated just as are those of Wales and Scotland. The two 

 sets of phenomena are so exactly identical that no one who has 

 ever compared them can doubt that they are dae to the same 

 causes. But we have farther and even more convincing evi- 

 dence. Glaciers produce many other effects besides these two, 

 and whatever effects they produce in Switzerland, in Norway, or 

 in Greenland, we find examples of similar effects having been 

 produced in our own country. The most striking of these are 

 moraines and travelled blocks. 



A GLACIER WITH MORAINfS. 



Moraines. — Almost every existing glacier carries down with it 

 great masses of rock, stones, and earth, which fall on its surface 

 from the precipices and mountain slopes which hem it in, or the 



