448 W/dtake?' — On Subaerial Denudation, 



illustration, it may be well to state that for the last ten years I have 

 been doing Geological Survey work in Cretaceous and Tertiary dis- 

 tricts ; work which has slowly convinced me against what I believed 

 before (as many of my colleagues have been in like manner convinced) 

 that the irregularities of the earth's surface have been chiefly caused 

 by subaerial actions, by rain rivers frost and springs, forces that 

 can be seen in action every day and therefore have come to be looked 

 on as things of nought. I do not say however that the sea has 

 done nothing towards the formation of these irregularities; but allow 

 that many of the present features may have been worked out and 

 strengthened along lines sketched out as it were beforehand by 

 the action of the sea, which is granted I believe by most who hold 

 the subaerial theory, although they are often misrepresented as deny- 

 ing that the sea does anything. In some cases the marks of marine 

 action may have been little effaced, but for the most part they must 

 have been destroyed when exposed for a long time to the wasting 

 powers that reign over the land. 



2. — Authors who have advocated the Subaerial Theory. 



It seems strange that there should now be any discussion on the 

 subject, and that instead of subaerial denudation being the accepted 

 theory of the day it should be held by a minority only (albeit that 

 minority contains many well-known geologists, and increases every 

 year) ; for the power of atmospheric actions in wearing away rocks 

 was most ably treated of more that 70 years ago by Dr. Hutton, 

 whose great work^ is not so well known as it should be, and indeed 

 is known mostly in a secondhand way, through Professor Playfair, 

 who followed and defended the views of his friend and master." 

 After this Mr. Scrope proved their truth for a special district, showing 

 that in Auvergne rivers have worn away large masses of hard rock,^ 

 and said that "the same agents (rain and rivers) must have been at 

 work everywhere else, and produced results as stupendous during 

 the same (comparatively) recent period," and " since, by a fortimate 

 concurrence of igneous and aqueous phenomena, we are enabled to 

 prove the valleys which intersect the mountainous district of Central 

 France to have been for the most part gradually excavated by the 

 action of such natural causes as are still at work ; it is surely in- 

 cumbent on us to pause before we attribute similar excavations in 

 other lofty tracts of country, in which, from the absence of recent 

 volcanos, evidence of this nature is wanting, to the occurrence of 

 unexampled and unattested catastrophes, of a purely hypothetical 

 nature." 



i The Theory of the Earth, 2 vols., 8vo. ; Edin., 1795. See especially vol. 1. p. 

 304 and vol. ii. pp. 3-5, 98, 99, 138-40, 143 (quotation from the French), 157, 205, 

 209! 210, 236, 245, 29.'), 296, 401, 466-8, 498, 528, 529, 534, 535, 547. 



2 Illustrations of the Huttonian Theory, 8vo. ; Edin , 1802. Eeprinted in vol. i. of 

 Playfairs Works, 1822. See pp. 105-7, 110-14, 373-6 of the original edition ( = pp. 

 117-19, 122-5, 370-2 of the later one. 



3 Memoir on the Geoh.gy of Central France, 4to., Lond., 1827. Ed. 2, 8vo., 1858 

 (pp. 37, 38) 97, 158, 159. 205-9, 213, 244 ; and Geol. Mag., Vol. III. p. 193 (1866). 

 Mr Scrope touched on the suhject before in his " Considerations on Volcanos," 8vo. 

 Lond., 1825 (pp. 96, 97, 138, 139, 214, 215). 



