1881.] Recent Literature. 307 
on the climate of the globe,-and to the question of past glacial 
epochs and their causes. Mr, Wallace while adopting generally 
Mr. Croll’s views as to the causes of the glacial epoch, limits and 
modifies his views by pointing out the very different effects on 
climate of water in the liquid and solid state, and that without 
high land there can be no permanent snow and ice. e con- 
cludes that the “alternate phases of precession, causing the winter 
of each hemisphere to be in aphelion and perihelion each 10,500 
years, would produce a complete change of climate only where a 
country was partially snow-clad; while, whenever a large area be- 
came almost w/ol/y buried in snow and ice, as was certainly the 
and adopts Sir William Thompson’s conclusion “ that the crust of 
the earth cannot have been solidified much longer than 100,- 
000, years ;” and Professor Haughton’s estimate that the time 
to be required to produce the maximum thickness of the stratified 
rocks of the globe (177,200 feet) at the present rate of denudation - 
and deposition is only 28,000,000 years. Now these are only 
Suesses, but yet are useful, as indicating the order of magnitude 
of the time required. Mr, Wallace therefore claims that “ so far 
as the time required for the formation of the known stratified 
rocks, the hundred million years allowed by physicists is not only 
ample, but will permit of even more than an equal perio anterior 
to the lowest Cambrian rocks, as demanded by Mr. Darwin.” 
“In the tenth edition of the Principles of Geology, Sir Charles 
Lyell, taking the amount of change in the species of mollusca as 
a guide, estimated the time elapsed since the commencement of 
the Miocene as one-third that of the whole Tertiary epoch, and 
the latter at one-fourth that of geological time since the Cambrian 
Period. Professor Dana, on the other hand, estimates the Ter- 
tary as only one-fifteenth of the Mesozoic and Paleozoic com- 
