ANNXVERSART ADDRESS OP THE PRESIDENT. IxXXVil 



ing the whole subject, Mr. Hopkins was led to the conclusion that 

 the existence of a central heat is not in itself sufficient to account 

 for the phenomena which terrestrial temperatures present to us. 



Are we, upon these grounds, to look to various scattered foci of 

 heat within the thickness of the earth's crust ? How, unless we 

 have the sources of lava and of high-pressure steam at a moderate 

 distance beneath the surface, is it possible to explain the action of 

 volcanos, and the undulation and contortion of the strata, whether 

 through elevation or, more generally, through depression? how, 

 with a crust hundreds of miles thick, or with a dense and solid 

 globe as upheld by Poisson and his followers, conceive of the phe- 

 nomena which mark the presence of mountain-chains around the 

 whole earth? And if there be but a crust, whether overlying a 

 liquid nucleus or limited seas of molten rock, is it probable that the 

 thickness will at diiferent places vary within wide limits ? I cannot 

 but think that we have much more to learn before the problem is ripe 

 for solution. Prof. Phillips well showed, some years ago, that 

 sundry conditions must be taken into consideration beyond the mere 

 couducting-power of rock-masses, and that convection, or transmis- 

 sion by means of water and air, plays at the present time the more 

 important part. In our copper-mines the chemical action of the sul- 

 phide ores manifestly gives rise to an abnormal temperature ; at equal 

 depths the air and rock of tin- and of lead-veins are cooler. And, 

 in juxtaposed mines, the same horizon shows so different a tempera- 

 ture, according to whether they be opened in granite or in clay-slate, 

 that we look upon the cooler condition and slower rate of increase of 

 temperature in the unstratified rock as somewhat in accordance 

 with the result of Hopkins's experiments. Yet, on taking into ac- 

 count the frequent alternation of these rocks within a small area, 

 and, more than all, on carrying our mental view downwards a few 

 thousand feet from the surface, and speculating on the small part 

 which must be played in depth by the stratified substances, we are 

 obliged to conclude that far more complete observation is greatly 

 needed. 



Geology has happily in the meanwhile an abundance of other 

 and more accessible problems for our study ; and, notwithstanding 

 the difficulty (at first sight almost insurmountable) of exploring the 

 nature of the globe far beneath where we can ever hope to penetrate, 

 marvels have already been accomplished in that direction. Not only 

 the actual presence, but the gradual history of the construction, of 

 miles on miles in thickness of parts of the crust have been so far 

 established that we may well afford to await the gradual develop- 

 ment of the physical and chemical inquiries by aid of which many 

 of these researches can alone be pursued. 



And now, gentlemen, in approaching the end of my task, I feel 

 perfectly conscious that I have touched only on the one side of our 

 great subject of geological science, and have almost omitted to men- 

 tion the other. This has not been for want of due consideration. 

 I reflected that a mass of palaeontological details imperfectly arranged 

 and set before you could profit little, and that I should best fulfil 



