460 
POPULAR SCIENCE REVIEW. 
any large amount of atmospheric denudation since that 
period. 
With the absolute certainty, then, that so little has been 
accomplished by atmospheric denudation in some parts of our 
island, how are we to believe that so much has been effected 
in others ? The reader is probably aware of the views of 
Professor Eamsay, Dr. Foster, and Mr. Topley regarding the 
atmospheric denudation of the Weald, that region of Kent 
and Sussex from which the Chalk and Lower Cretaceous groups 
have been swept away, laying bare the Wealden formation.* 
It is supposed, however, that this region was unsubmerged 
during the Drift period, and therefore that the rains and rivers 
have had a much more extended period of uninterrupted 
work than in the northern parts of the island. But this is 
by no means certain in itself, and the difficulty still remains 
of accounting for the terraced aspect of some parts of the 
country, which, as I have endeavoured to show, is incompa- 
tible with the view of atmospheric denudation. In the region 
of Auvergne, in Central France, which has been so faithfully 
described by Mr. Scrope, the amount of denudation by the 
rains and rivers has certainly been on a most extended scale ; 
but in this case these agents have acted apparently without 
interruption since the latter part of the Tertiary period. In 
the south-west of Ireland, however, where Mr. Jukes has 
come to the conclusion that many of the river valleys are alone 
due to the rivers themselves, this has not been the case, as 
the country was certainly, to a large extent, submerged at the 
Drift period : how this fact can be reconciled with his views I 
am not in a position to state, but the sea having been there, it 
could scarcely have departed without leaving impressions on 
the surface. 
The arguments, however, advanced by my colleagues of the 
Geological Survey in favour of the atmospheric denudation of 
the Weald are certainly very forcible, and seem to account for 
the fact that the rivers generally cross the chalk escarpments 
transversely, instead of making their way to the sea along 
their bases. And if it be allowed that this rain and river 
action has been in operation uninterruptedly since the Eocene 
period, it is impossible to estimate the effects which might be 
produced throughout so vast a lapse of time. 
I hope the reader will not conclude from the above that I 
call in question the power of atmospheric agencies to produce 
considerable modifications of the earth's surface under certain 
# See Professor Ramsay’s “ Physical Geology,” 2 Edit., p. 79, &c. 
Messrs. Foster and Topley, Quarterly Journal of the Geological Society of 
London , vol. xxi., p. 460. 
