THE ICE AGE AND ITS WORK 



67 



above the fine moraine already mentioned, and in many 

 other places around the same mountain. On the whole, 

 considering their abundance in all glaciated regions, and 

 the amount of information they give as to the direction 

 and grinding power of ice, these rounded rocks afford one 

 of the most instructive indications of the former 23resence 

 of glaciers ; and we must also agree with the conclusion of 

 Darwin (in a paper written after studying the phenomena 

 of ice action in North Wales, and while fresh from his 



Fig. 12.— striated rock-surface at wasdale crag. 



observations of glaciers and icebergs in the southern hemi- 

 sphere) that " one of the best criterions between the effects 

 produced by the passage of glaciers and of icebergs is 

 boss or dome-shaped rocks." (Fig. 11.) from the United 

 States Geological Survey Reports, is a fair illustration 

 of roches motitonndes. 



(3) Striated, grooved, and fluted rocks, though closely 

 connected with the preceding, form a distinct kind of 

 evidence of the greatest value. Most of the bosses of 



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