SIGNS OF FORMER GLACIATION. 125 



inequalities of the country. From this comparatively solid 

 character of ice certain important results must follow. It 

 is easy to see that the stones of all sizes, while being dragged 

 along underneath the ice, would be held in a comparatively 

 firm grasp so as to be polished and striated and scratched in 

 a peculiar manner. On the shores of bays and lakes and in 

 bottoms of streams we find that the stones are polished and 

 rounded in a symmetrical manner, but are never scratched. 

 The mobility of water is such that the edges and corners of 

 the stones are rubbed together by a force acting successively 

 in every possible direction. But in and under the ice the 

 firm grasp of the stiff semi-fluid causes the stony fragments 

 to move in a nearly uniform direction, so that they grate 

 over the underlying rocks like a rasp, wearing down the 

 rocks beneath and slowly grinding them to powder, and, 

 at the same time, being worn themselves in the process. 

 From the stability of the motion of such a substance as ice 

 there would, from the nature of the case, result groovings 

 and striation both on the rocks beneath and on the bowlders 

 and pebbles which, like iron plowshares, are forced over 

 them. Scratched surfaces of rock and scratched stones are 

 therefore, in ordinary cases, most trustworthy indications of 

 glacial action. The direction of the scratches upon these 

 glaciated bowlders and pebbles is, also, worthy of notice. 

 The scratches upon the loose pebbles are mainly in the direc- 

 tion of their longest diameter — a result which follows from 

 a mechanical principle, that bodies forced to move through 

 a resisting medium must swing around so as to proceed in 

 the line of least resistance. Hence the longest diameter of 

 such moving bodies will tend to come in line with the direc- 

 tion of the motion. 



A scratched surface is, however, not an infallible proof 

 of the former presence of a glacier where such a surface is 

 found, or, indeed, of glacial action at all. A stone scratched 

 by glacial forces may float away upon an iceberg, and be 

 deposited at a great distance from its home. Indeed, ice- 

 bergs and shore-ice may produce, in limited degree, the phe- 



