Wynne — Denudation and its Causes, 3 



n. — On Denudation with reference to the Configuration of 



THE Ground. 

 By A. B. Wynne, F.G.S., &c. 

 (PLATES I. AND II.) 

 JNTBODUCTION.— The consideration of the subject of Denuda- 

 tion requires so extensive an acquaintance with Forms of the 

 Ground in a field large enough to embrace all countries, that general 

 conclusions must be advanced with more or less reserve, in pro- 

 portion to the extent of our research. 



What we know concerning the external features of other worlds 

 throws but little light upon the manner in which those of our earth 

 were formed. From astronomers we learn, indeed, of mountains and 

 valleys in the moon,^ of more peculiar forms than those commonly 

 occurring upon the earth ; and differing from them in their manner 

 of arrangement ; but we have here totally different conditions in the 

 supposed absence both of water and atmosphere, while the crater- 

 like aspect of the elevations renders them comparable to but one 

 kind of terrestrial mountains, and that the least connected with 

 denudation. We hear also of great mountains upon some of the 

 planets, those in Venus being supposed to have the enormous height 

 of twenty-two miles.^ In this case an atmosphere is believed to exist, 

 but whether these mountains have a similarity to those of our satel- 

 lite, or bear signs of denudation like those of the earth, remains un- 

 certain. 



On the earth, however, whether from difference of causes or 

 different developments of some similar agencies, the features, though 

 smaller, are yet of sufficient grandeur, and surrounded by mysterj^ 

 enough to invest with considerable interest enquiries into the 

 methods of their production. 



Denuding Agencies. — The various features which the land presents 

 are generally understood to have been produced by a comparatively 

 limited number of causes, sometimes simple in their action, but vast 

 in their results ; they are principally chemical changes, aqueous denu- 

 dation, and the action of volcanoes in heaping up mountains of a par- 

 ticular kind. Of these, if denudation, either sub^rial or marine, be 

 taken as the immediate and principal cause of the configuration of 

 the ground, a more remote but not less necessary agency is to be 

 attributed to forces of elevation and also of depression — having 

 brought different portions of the land within reach of erosive action. 



Antiquity of these Agencies. — It would be going too far back to spe- 

 culate upon the probability or otherwise of our planet having ever 

 presented a smooth unbroken surface in every part ; enough that at 

 incalculably remote periods land and water existed upon it ; that in 

 the water silts, sands and gravels were deposited, and that, there- 

 fore, denudation was taking place upon the land to an extent, some 

 idea of which may be arrived at from the great thickness of aqueous 

 formations known to Geology at present. 



^ Geology of the Moon. — Geol. Mag., Vol. iii., p. 141. 

 ^ Wm. Carter, M.B., Plurality of "Worlds.— Quart. Jour. Science, p. 232. 



