THE ICE AGE AND ITS WOKK 



Island. These exhibit not only the pliancy of the ice, but at 

 the same time its strong hold upon the armature with which it 

 did its work of abrasion, grooving, and striation. For, while these 

 grooves can scarcely be supposed to have been originated de novo by 

 the gouging action of the ice, they are, nevertheless, ploughed with 

 deep furrows, the symmetry, continuity, and peculiar form of some 

 of which are only intelligible on the supposition that they were cut 

 by a single graving tool, held with sufficient tenacity by the ice to 

 execute by a single movement a deep, sharply-defined groove. 

 There is, perhaps, no finer illustration of the pliancy with which the 

 ice yielded to its encompassing barriers, the tenacity with which it 

 held its armature, and withal the pressure that both forced it into 

 compliance with its tortuous channel, and pressed it relentlessly 

 forward." ^ 



Kelly's Island is at the western end of Lake Erie, and 

 in the direction of the striae to the north-east there is no 

 high ground for about 400 miles. Looking at these facts, 

 I cannot give any weight to the opinions of these who, 

 from observations of existing glaciers, declare positively 

 that ice cannot go up-hill, and can exert no grinding power 

 on level ground. 



The two photo-plates here given show, however, that 

 we possess equally fine illustrations of ice-grooving in 

 our own country. Fig. 13, kindly given me by Mr. Percy 

 F. Kendall, well shows the size of the grooves by com- 

 parison with the boy's body. It was taken at Barmouth, 

 N. Wales. The other (Fig. 14), I believe at the same 

 place, shows how the ice has been forced into curves by 

 the general form of the rock surface, a phenomenon that 

 indicates a slow-moving plastic material such as glacier- 

 ice is proved to be, and which could not have been caused 

 by any other known agency. The highly polished surface 

 of the rock is well shown in the photograph, though in a 

 less degree in the reproduction. 



Erratics and Perched Blocks. 



(4) Erratic blocks were among the phenomena that first 

 attracted the attention of men of science. Large masses 

 of granite and hard metamorphic rock, which can be 



^ Seventh Annual Report of the United States Geological Survey, p. 

 179 (Fig. 17). Arrangements have now been made for the preservation 

 of these remarkable examples of ice work. 



