382 DAVIS — PLAINS OF MARINE AND SUBAERIAL DENUDATION. 



That an author who has so ably discussed the relative competence of 

 marine and subaerial denudation should not give explicit account of 

 plains worn down under the air and afterward uplifted and dissected, 

 illustrates how strongly the doctrine of marine denudation has been im- 

 pressed on the geologists of today. 



Brief citation may be made from a number of other books and essay's. 



The able article, "The Denudation of the Weald,"* in which Foster 

 and Topley did so much to advance the modern understanding of the 

 subaerial origin of valleys, assumed that the streams of southern England 

 began to act on an uplifted plain of marine denudation, and from this 

 arbitrary beginning explained the transverse valleys by which the chalk 

 escarpments around the Weald are trenched (page 473). 



Maw in his essay, "Notes on the comparative structure of surfaces 

 produced by subaerial and marine denudation," f contrasts hills and 

 valleys carved by rain and rivers with 2)lains of denudation carved by 

 the sea. 



In the same way Wynne wrote " On denudation with reference to the 

 configuration of the ground " X and concluded that — 



" Rain seems to act vertically, its tendency always being to produce steep ground 

 where it is not accumulating materials. Thus we are obliged, in the absence of 

 anything more likely to produce then], to attribute the formation of plains to the 

 action of the sea" (page 10). 



A little later Whitaker, when advocating the origin of cliffs and escarp- 

 ments by subaerial denudation, said that nature "uses the sea to carve 

 out continents and islands ; rain and rivers to cut out hills and valleys." § 



Mackintosh in his " Scenery of England and Wales" (1869) carries the 

 doctrine of marine erosion to an extreme and allows hardly anything to 

 subaerial agencies. Even the inner Triassic lowlands of England, inside 

 of the oolitic escarpment, are ascribed to marine denudation. " The sea 

 must have mainly given rise to the inequalities of the earth's surface, so 

 far as they are the result of denudation " (page 292). 



It appears, therefore, that the active discussion in England, of which 

 the above extracts give some indication, did not consider the possibility 

 of subaerial baseleveling, but was concerned chiefly with the origin of 

 valleys by rain and rivers. Since the settlement of this question, land 

 sculpture has not received much attention from English geologists, as the 

 following extracts from a later period will show. 



Green says, " the even surface that would result from the action of 



* Quart. Journ. Geol. Soc, vol. xxi, 1865, pp. 44:^-474. 

 tGeol. Magazine, vol. iii, 1806, pp. 439-451. 

 JGeol. Magazine, vol. iv, 1867, pp. 3-10. 

 g Geol. Magazine, vol. iv, 1807, p. 454. 



