38 ON CHANGES IN THE DISPOSITION 



were not originally deposited in those places as else- 

 where. It is proved, among '^inclined and incurvated 

 strata, when the outer and lower' beds are wanting in 

 a tract of concave strata, and the outer but upper ones 

 in a convex series. Thus, at Crowborough hill in Sussex, 

 the strata above the ferruginous sand are deficient on 

 each side ; while, near London, the deficient strata are 

 those beneath the clay. Although in England, in 

 many places, a great depth of stratified rocks lies above 

 the coal series, they disappear in Scotland ; whence, 

 in that country, it is almost every where uppermost. 

 We cannot indeed prove that it has not always been 

 so ; but from the great loss of strata in this part of 

 the island, the contrary is most probable. 



There is one evidence of denudation, which, though 

 limited to a few tracts, demands notice, especially, here, 

 from indicating a cause which has been either unsus- 

 pected, or to which very inferior powers to that which 

 it possesses have been assigned. This is the persist- 

 ence of Trap veins, much more rarely of granite ones, 

 after the surrounding strata have disappeared : thus 

 remaining an index, if not a measure, of that waste 

 which their harder nature has enabled them to resist. 

 Near Comrie, two of these, of great dimensions, hold 

 a parallel course for many miles, rising high, in many 

 places, above the surrounding land ; and, in the great 

 Cumbray, one not less remarkable from its curvature 

 than its elevation, crosses the island; a magnificent 

 wall from the hand of Nature, and a beacon of the 

 waste which the including sandstone has experienced. 

 A similar one in Isla, holding its uninterrupted course 

 over hill and valley, produces, at first, the deceptive 

 effect of some gigantic work of architecture. But 

 none are so striking as that great wall of pitchstone 

 which forms the Scuir of Egg ; a descried vein, indi- 



