466 Transactions. — Geology. 



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 w^ere due to 

 other causes 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 common 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- 



