304 Dr. C. Ricketis—Oscillation of the Earth’s Crust. 
entitled “Physics of the Earth’s Crust,” 1881, have commented on 
the occurrence of subsidence during the deposition of the different 
geological formations ; and also where accumulations are in progress 
at the present time under the sea; or on land covered with a heavy 
load of snow, as in Greenland. They agree with me in considering 
the depression as the result of and caused by the weight of the 
accumulations. (I must express how greatly I feel indebted to 
these authors for the courtesy with which they have recognized 
such deductions made by myself as far back as 1865,' and more 
especially at various periods since 1871.”) They agree with me in 
considering the depression as the result of and caused by the weight 
of the accumulations. Mr. Fisher considers ‘‘it requisite for the 
explanation of the phenomena that there be a liquid, or at least 
a plastic substratum for the crust to rest on; nor is it easy to 
explain the sinking of areas in proportion to their becoming over- 
loaded with sediment upon any other supposition; but if such a 
liquid substratum be granted, many of the facts are more easily 
explained. If the present configuration of the Himalayan region 
be one of approximate equilibrium, if much sediment be brought 
off the mountains and spread over the plains, the mountains must 
become after a while too light and the plains too heavy; and 
accordingly the mountains rise and the plains sink to restore the 
contour”’* (or equipoise). 
It is now almost universally acknowledged that valleys have been 
excavated by subaerial agencies, and that the materials which once 
filled up the vacancies have been removed by rain and rivers, and 
carried down and deposited near the mouths of their respective 
rivers and neighbouring parts of the sea. Towards the mouths of 
large rivers every one knows the bottoms of the valleys are filled 
with detritus brought down by the stream; these deltoid accumula- 
tions being often not only of great width, but also of very consider- 
able thickness. According to Sir Charles Lyell,* the thickness has 
been proved by borings to be more than 630 feet in the case of the 
Mississippi; but he considers it probable that it may have attained to 
twice or thrice that thickness ; in the case of the Ganges, the depth 
reached was 481 feet; and in the Po 400 feet; each example afford- 
1 A Ramble in Shropshire, Proc. Birkenhead Lit. and Scient. Soc. 1865; A 
Wooden Implement found in Bidston Moss, Proc. Liverpool Geol. Soc. 1865-66. 
2 President’s Address, by Charles Ricketts, Proc. Liverpool Geol. Soc., Session 
1871-72. Also an abstract of the same, entitled ‘‘On Subsidence as the Effect of 
Accumulation,’’ Grou. Mae. Vol. IX. p. 119, ete. 
3 Physics of the Earth’s Crust by the Rev. Osmond Fisher, M.A., F.G.S., p. 83. 
Referring to the Himalayan region, it was stated by myself in 1875, when replying 
to objections which had been raised, that the removal by denudation of those 
portions of the mass which once filled up the spaces now iorming the valleys and 
passes of this great mountain range, must have diminished proportionately the amount 
of weight pressing upon the fluid substratum. Should the sediment brought thence 
by the Ganges and Brahmapootra, and deposited in the Bay of Bengal, cause sub- 
sidence by its weight, it follows that the area from which the sediment has been 
derived must rise in proportion to the amount of material removed.—The Cause of 
Cae cease Period, by Charles Ricketts, Guon. Mac. Dec. II. Vol. II. p. 474, 
OOT-NOLE. 5 
4 Principles of Geology, vol. i. chapters 18 and 19. 
