182 ON THE REVOLUTIONS 



with cases in which the surface of the rock has been dressed to 

 smoothness, and in which the abrasion shews itself in tlie ge- 

 neral rotundity of the grooves and scoopings, and in the obtuse 

 angled and waving ridges just described *. 



But what I have hitherto looked for in vain in common ri- 

 vers, occurs universally in the diluvian scenes, where there is 

 reason, from other circumstances,to believe, that a powerful abra- 

 sion has taken place, and where the surface has been protected 

 from the injuries of the weather. Where it has been exposed 

 to that injury, we generally find, that the large features of 

 dressing, the grooves and scoopings, and obtuse-angled ridges, 

 only reinain. But where a mass of this kind, either by acci- 

 dent or design, has been followed under ground to where its 

 surface has been protected by a covering of clay, an interest- 

 ing and striking scene presents itself; the surface is found to 

 resemble that of a wet road, along which a number of heavy 

 and irregular bodies have been recently dragged ; indicating 

 that every block that passed, and every one of its corners, had 

 left its trace behind it ; and these are rendered very distinctly 

 visible, when the surface is drenched with water. 



In many cases these furrows or scratches have been so deep 

 as to resist all the effects of the weather, and shew them- 

 selves in rocks that have been always exposed, sometimes 



many 



* The only case which has as yet occurred to me, bearing any relation to the 

 action here alluded to, arose from a cause seemingly quite insignificant. In a 

 neighbouring county, a country house, situated upon the slope of a hill, was as- 

 sailed by a sudden torrent of water, produced by the bursting of a thunder-storm 

 on the hill above. The impetuosity of the stream was such, that it forced its 

 way through the under storey of the house, carrying along with it quantities of 

 sand and gravel, and stones of considerable bulk. Happening to be upon the 

 spot a few weeks after the accident took place, I observed, that every stone, as 

 it passed through the house, had left a rut or scratch behind it, upon the flags 

 ever which it passed. 



