224 Professor Agiissiz on the Glacial Theory. 



mena were attributed to the action of water, no endeavour 

 was made to search for another cause for the transport of er- 

 ratic blocks. But if a comparison had been instituted between 

 the pohshed surfaces and the effects produced by currents, very 

 remarkable differences between them would have been dis- 

 covered. As I have said elsewhere, rocks polished by glaciers 

 of the present day present surfaces gently rounded, smooth, and 

 continuous over large spaces, sometimes even perfectly flat, and 

 passing uniformly over the most resisting portions of rocks as 

 over the softest, without forming sinuosities or edges. They 

 are, moreover, furrowed, in the direction of the movement of 

 the glacier, by furrows more or less deep and rectilinear, and 

 scratched by fine strias, perfectly rectilinear, and evidently 

 parallel to one another and to the furrows ; and, when the 

 latter offer deviations from the general direction of the valleys, 

 it is in consequence of circumstances which it is easy to ap- 

 preciate. Such are likewise the polished surfaces remarked 

 at the bottom and on the flanks of the valleys which are en- 

 compassed by erratic blocks and moraines, even when they 

 are no longer occupied by glaciers. But such are not the ap- 

 pearances exhibited by rocks worn by water ; although smooth 

 they are never polished, and their undulated and sinuous sur- 

 faces present hollows or irregular excavations wherever the 

 nature of the rock favoured erosions ; no portion of the sur- 

 faces worn by currents of water has exhibited to me those 

 long rectilinear striae so characteristic of the polishing of gla- 

 ciers. These differences between the abrasion occasioned by 

 glaciers and that caused by water, are very well explained by 

 the difference presented by a current of water, which, while 

 it bounds along, follows all the sinuosities of its bed, and a rigid 

 mass of ice which advances slowly on account of its consist- 

 ence. The conformity which I have already pointed out be- 

 tween the aspect of polished valleys whose flanks are charged 

 with erratic blocks together with continuous mounds, and whose 

 mouths are closed by concentric barriers of blocks, and the 

 aspect of the valleys at present occupied by glaciers flanked 

 by their lateral and terminal, ancient and recent moraines, 

 and whose bottoms are polished, striated, and furrowed in the 

 direction of the movement of the glacier ; this conformity, I 



