Vice-President’s Address. 261 
case do they show any sign of having acted with greater 
energy than they do at the present day. In short, even as 
far back as the commencement of the Cambrian Period, the 
two great geological factors, solar energy and gravitation, 
appear to have operated then very much as they do now. 
To a geologist this merely indicates that the close of what 
has been termed the Astronomical History of the Earth 
terminated many millions of years prior to the Cambrian 
Period, and that the Earth must have been in a condition 
suitable for life through a long period of the time when the 
Archean rocks were in process of formation. 
Turning to the records supplied by fossils, we find that 
the life-conditions during Lower Cambrian times were in no 
respect yet discovered different from what such conditions 
are to-day. Organisms then, as now, changed under the influ- 
ence of varying environment and other biological factors at, 
apparently, at least as slow a rate as now. Hence biologists 
concur with geologists in claiming, as requisite for the develop- 
ment of the existing forms of life, an interval of time fully 
as vast as that required to account for the physical changes 
which are known to have taken place upon the earth, 
It is true that some there were, and perhaps there may 
be some still, who, taking note of these facts relating to the 
Earth’s history, declared that they could perceive no vestige 
of a beginning, and no prospect of an end. It was only 
natural that a reaction should set in against views so directly 
opposed to all that we know through the researches of the 
astronomer. Mathematicians and physicists of eminence 
took up the question, and discussed it from their own stand- 
points, basing their conclusions upon what, at the time, 
appeared to be well-established facts. The conclusions 
referred to were by no means identical with those to which 
geologists had been led. Lord Kelvin, for example, boldly 
stated his opinion that all geological history showing con- 
tinuity of life must be limited within some such period as 
100,000,000 of years; and Professor Tait was disposed to 
allow even very much less than that. Lord Kelvin has 
lately considerably modified the view here referred to,’ but 
1 “Nature,” vol. li., 1895, p. 257. 
