292 On the Glacial Theory^ 



But, whatever may be the abrasive power of water, it has 

 never been shown that a stone propelled by water can make 

 furrows and scratches upon the rocks with which it may come 

 in contact. We believe this is physically impossible ; and 

 that, if it did exist, there are no rivers which would not afford 

 numerous examples of such furrows and scratches. Rocks 

 might be polished, gravel might be formed, if water had the 

 power of abrasion ; or these might be produced by the fric- 

 tion of stones upon each other, if continued long enough ; but 

 a furrow or a scratch can only be made under a pressure 

 sufficient to overcome the cohesive force of the' particles of the 

 body acted upon. When we have the moving power at will, 

 we can, by increasing it, cause a less dense body to mark a 

 denser one. We can force a candle through a deal of wood, 

 or a leaden bullet through a plate of iron ; but where the 

 power is a stream of water, whose velocity practically lies 

 within a very limited range, and when the body moved is a 

 rock or stone, which has lost by its emersion from one-half 

 to one-third of its weight, the force with which it im- 

 pinges against any obstacle in a stream, however impetuous, 

 must be comparatively very slight, and wholly insufficient to 

 produce a furrow *' six feet long, an inch wide, and one-third 

 of an inch deep," as found on Arthur's Seat. 



Nor will time render any assistance in this operation. 

 The grooves and scratches clearly indicate that their forma- 

 tion was completed at one stroke of the tool, and not by 

 a succession of strokes with different tools. Indeed, the 

 probability of two or more stones moving along the side of a 

 rock exactly in the same place, is so very remote, that it 

 cannot for an instant be seriously entertained. 



We need not discuss this question with reference to the 

 grooves and scratches which are found upon the sides of rocks 

 several hundred feet above the bed of the valley beneath, and 

 thousands above the level of the sea. For if it be clearly 

 shown that water has the power of producing them in the 

 lower situations where they are found, that is all that can 

 fairly be required from the opponents of the theory ; without 

 asking them to show from whence such a body of water came 



