28 EVOLUTION 
found to show a very fair measure of agreement, and 
they led to the conclusion that considerably less than 
a hundred million years has elapsed since the first for- 
mation of seas upon this planet, an event which must 
have preceded the possibility of aqueous geological 
action and the existence of living organisms 
Allowing for the circumstance that geological pro- 
cesses may have gone forward with considerably 
greater rapidity during the earlier periods of the 
earth’s history than is the case at the present day, the 
time thus allowed by the physicist is generally regarded 
by geologists as too little. Reckoning from the known 
rate of denudation, which is, of course, the same as 
the rate at which the same material is deposited 
beneath the sea, Geikie, who admitted, however, that 
such data are only of a very rough description, 
concluded that the space of a hundred million years 
would afford sufficient time for the laying down 
of the known aqueous strata. But there can be 
little doubt that the lower metamorphosed rocks 
represent a much longer period of time than 
the primary, secondary, and tertiary epochs added 
together; consequently, the respective estimates of 
Lord Kelvin and the geologists appear to be contra- 
dictory. The recent discovery of the enormous quan- 
tities of energy stored up in radio-active substances 
introduces a serious modification into the mathematical 
argument from astronomical data, and Sir George 
Darwin ‘sees no reason for doubting the possibility 
of augmenting the estimates of solar heat, as derived 
from the theory of gravitation, by some such factor 
