INORGANIC GEOLOGICAL DYNAMICS. 54:7 



ture on a small scale, which is common in the solid ice of the glacier. 

 The planes of these ribbons are, for the most part, at right angles t 

 the crevasses, near the sides of the glacier, while, near its central line, 

 they dip towards the upper part of the glacier. This structure appears 

 to arise from the difference of velocities of contiguous moving 

 filaments of the icy mass, as the crevasses themselves arise from the 

 tension of larger portions. Mr. Forbes has, in successive publications, 

 removed the objections which have been urged against this theory. In 

 the last of them, a Memoir in the Phil. Trans., 1846, (Illustration 

 of the Viscous Theory of Glacier Motion,} he very naturally expresses 

 astonishment at the opposition which has been made to the theory on 

 the ground of the rigidity of small pieces of ice. He has himself 

 shown that the ice of glaciers has a plastic flexibility, by marking 

 forty-five points in a transverse straight line upon the Mer de Glace, 

 and observing them for several days. The straight line in that time 

 not only became oblique to the side, but also became visibly curved. 



Both Mr. Forbes and other philosophers have made it in the highest 

 degree probable that glaciers have existed in many places in which 

 they now exist no longer, and have exercised great powers in trans- 

 porting large blocks of rock, furrowing and polishing the rocks along 

 which they slide, and leaving lines and masses of detritus or moral f 

 which they had carried along with them or pushed before them. It 

 cannot be doubted that extinct glaciers have produced some of the 

 effects which the geologist has to endeavor to explain. But this- part 

 of the machinery of nature has been worked by some theorists into an 

 exao-gerated form, in which it cannot, as I conceive, have any place in 

 an account of Geological Dynamics which aims at being perma- 

 nent. 



The great problem of the diffusion of drift and erratic blocks from 

 their parent rocks to great distances, has driven geologists to the con- 

 sideration of other hypothetical machinery by which the effects may 

 be accounted for : especially the great northern Irift and boulders, 

 the rocks from the Scandinavian chain which cover the north of Europe 

 on a vast area, having a length of 2000 and breadth of from 400 to 800 

 miles. The diffusion of these blocks has been accounted for by sup- 

 posing them to be imbedded in icebergs, detached from the shore, 'and 

 floated into oceanic spaces, where they have grounded and been depo- 

 sited by the melting of the ice. And this mode of action may to some 

 extent be safely admitted into geological speculation. For it is a mat- 

 ter of fact, that our navigators in arctic and antarctic regions have 



