THE ICE AGE AND ITS WORK 



71 



De Luc that the largest blocks were often found at the 

 greatest distance from the parent rock, and that this 

 fact was conclusive against their having been brought 

 to their present position by the action of floods. 



Erratic Blocks in Switzerlaoid . 



It is, however, in Switzerland that we find erratic 

 blocks which furnish us with the most conclusive testi- 



FlG. 14. — ROCK-GROOVINGS NEAR BARMOUTH. 



mony to the former enormous extension of glaciers ; and 

 as these have been examined with the greatest care, and 

 the facts, as well as the main inductions from the facts, 

 are generally admitted by all modern ^vriters, it will be 

 well to consider them somewhat in detail. It will be 

 found that they give us most valuable information both 

 as to the depth and extension of ancient glaciers, and 

 also as to the possibilities of motion in wide-spreading 

 ice-sheets. 



