Outlines of Geology. 257 



where the summits are not volcanic, are either of granite or its 

 modifications and associates. Now it is not impossible, and 

 experience renders it probable, that these exposed peaks have once 

 been covered, like their fellows in the lowlands, with some, or 

 perhaps with the greater number, of the rocks which we have 

 enumerated in the order of their superposition, but that these 

 have yielded to the ruthless lingers of time and the elements ; 

 that they have been degraded and washed away, and that the 

 denuded and indurated materials which they once covered, now 

 stand the more durable, but still decaying, monuments of that 

 former order of things ; the valleys, we are told, are filled 

 with the debris of the bordering hills, and the streams and rivers 

 wash them into the ocean, and are gradually tending to reduce 

 the surface of the earth to an unvaried plane. Lakes are 

 filling up ; bars are forming at the mouths of rivers ; mud is 

 gradually raising itself into dry land susceptible of cultivation, 

 and the unfathomable depths of the ocean will one day or other 

 become soundings, and ultimately, the waters of the sea will 

 overwhelm the land, and man's dominion will be no longer 

 suffered upon earth; or perhaps, to take the more cheering 

 prospect, subterranean fires may again consolidate and elevate 

 the detritus, and new islands and continents may arise out of 

 the ruins of their predecessors. 



Although these, and similar flighty hypotheses, deserve in them- 

 selves no serious consideration, they lead us naturally to inquire 

 as to the cause of those irregularities which the surface of the 

 earth exhibits — the origin of hills and dales, of mountains and of 

 valleys : but let us first temper our minds for the consideration of 

 this subject, by recollecting the extreme insignificance of these ir- 

 regularities, and the paltryness of what we are regarding as most 

 sublime and magnificent, compared with the bulk of our planet, 

 to which they are but as particles of dust upon the surface of an 

 artificial globe. In speaking of the transportation of granite 

 boulders, I have already adverted to the probable non-existence, 

 at the period of their lodgement in their present situations, of 

 several of the deepest and most extensive valleys of the world ; 

 and if we examine the walls, as it were, of these valleys, or at 



