466 Transactions.—(G eology. 
to the presence of water on our planet. Our planet, in common with the 
sun and the other members of the system, is moving through space at the 
rate of four to five hundred thousand miles a day, and must, if the 
hypothesis of an universal atmosphere be correct, to the extent of its 
gravitation force, daily obtain from this universal atmosphere a fresh 
supply of water. Now this supply will be equal to that which can be 
obtained from the contents of a cylinder of this atmosphere, the length 
of which is from four to five hundred thousand miles by nearly eight 
thousand in diameter. 
This is an interesting question, into which, however, it is unnecessary 
for me to enter, even if I possessed the elements necessary for the calculation 
of the probable quantity of water, if any, annually added to that upon our 
globe from this source. 
Let me now enquire how far geological evidence can be adduced in 
support of the view that heat, radiated during the cooling of our globe, 
affected climate during the earlier periods of life upon it. 
In dealing with this subject I propose to accept what has been given to 
us by Sir Charles Lyell in his great work already alluded to, in regard to 
the character of the life forms during past geological periods. 
In the tenth and eleventh chapters of the tenth edition, published in 
1867, the characters of the climate during the several periods extending 
from times immediately anterior to the historical, up to the Silurian period, 
is very fully discussed, and the author commences by commenting upon the 
objections which had been raised to the theory which endeavours to explain 
past geological changes by reference to causes now in action, pointing out 
that one of those objections is founded on the former prevalence of climates 
hotter than those now experienced in corresponding latitudes. I have before 
observed, however, that Sir Charles entirely repudiated the idea that during 
any portion of the time which has elapsed since life appeared on our globe, 
climate was affected by the heat radiated from the globe itself as the result 
of the cooling of its mass ; and his whole argument is founded upon the as- 
sumption, that the changes which had evidently taken place were due to 
other eauses than the one referred to. 
I will not trouble you with references to times prior to the Pliocene 
period. With regard to that period, however, and more especially to 
its lower strata, in eommon with those of the Upper Miocene, we learn 
that the fauna and flora of the whole of Central Europe afford unmis- 
takable evidence of a climate approaching that which is now only ex- 
perienced in sub-tropical regions ; and it is a matter of no small interest 
to know that when the climate of Europe was sub-tropical, a still greater 
. heat prevailed nearer the equator, as specially evidenced by the investiga- 
