The Glacial Theory. 



135 



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, more- 

 over, furrowed, in the direction of the movement of the glacier, by 

 furrows more or less deep and rectilinear, and scratched by fine 

 striae, perfectly rectilinear, and evidently parallel to one another and 

 to the furrows ; and, when the latter offer deviations from the gene- 

 ral direction of the valleys, it is in consequence of circumstances 

 which it is easy to appreciate. Such are likewise the polished sur- 

 faces remarked at the bottom and on the flanks of the valleys which 

 are encompassed by erratic blocks and moraines, even when they 

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

 ances exhibited by rocks worn by water ; although smooth, they are 

 never polished, and their undulated and sinuous surfaces present 

 hollows or irregular excavations wherever the nature of the rock 

 favoured erosions ; no portion of the surfaces worn by currents of 

 water has exhibited to me those long rectilinear striae so charac* 

 teristic of the polishing of glaciers. 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 

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

 tween the aspect of pohshed 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 po- 

 lished, striated, and furrowed in the direction of the movement of 

 the glacier ; this conformity, I say, is the principal argument that 

 has caused me to attribute to the existence of glaciers which no 

 longer remain, the phenomena similar to those produced by the 

 glaciers of the present day, and which we meet with in so many 

 localities far distant from glaciers. The granitic and porphyritic 

 rocks of many valleys in Scotland exhibit polishings equally bril- 

 liant with those at present observed on the slaty serpentines of the 

 flanks of the glaciers of Monte Rosa."* 



* Edinb. New Phil. Journ. No. 6G, p. 222. 



