64 



Such and so limited are the means of ChemistrVj that of many sub- 

 stances thus brought within the sphere of our inquiries, the point of 

 fusion is at this day unascertained. The author of the masterly publica- 

 tion before adverted to, brought together many useful observations 

 upon this subject. He observes that " Lavoisier could not melt a 

 " particle of Carbonate of Lime by the intense heat of a burning mir- 

 " ror, and that Quartz, according to Saussure, requires for its fusion 

 " a temperature = 4043° of Wedgwood's pyrometer^ Glass requiring 

 " at a medium only 30° of the same scale." 



That the Difficulty, which here suggests itself, of providing, in the 

 absence even of imaginary fuel, a Supply of imprisoned Heat sufficient 

 to fuse the substances I have mentioned and others scarcely less re- 

 fractory, may be mitigated by extending the time employed in the 

 process, or by the aid of compression and other circumstances, I am 

 ready to admit; but, in the most favourable view of the case, the Heat 

 wanted, (when we consider the thickness and extent of these rocks, 

 comprising entire mountains and mountain chains,) must be prodi- 

 gious ; and I cannot but admire the singular taste of those geological 

 speculators, who, enjoying the free range of the globe, have deposited 

 their Caloric exactly in that spot in which it can be of least use to 

 them. The inconvenience of this distribution becomes still more ap- 

 parent when it is recollected that fusion is not all that is necessary ; 

 but that, when fused, these substances must be propelled in a deter- 

 minate direction and with sufficient force, in many instances, to raise 

 the bed of the sea to the height of an Alpine chain. I will not at- 

 tempt to point out to you the way in which this is accomplished, but 

 confess at once that I do not understand it. 



And yet it appears certain that the surface of our planet has become 

 cooler and cooler, from the period when organic life commenced to 

 the tertiary epoch. If this cannot be explained by the Escape of Heat, 

 there remains only one other mode of explaining it, — a continually 

 diminishing Supply. The latter is the explanation offered by Mr. 

 Lubbock. Sir John Herschel, also, has brought into view causes 

 within the range of physical astronomy which, independently of a Loss 

 of Internal Heat, produce a slow but certain Diminution of Tempe- 

 rature on the surface of our globe*. These auxiliaries, however, are 

 insufficient. 



Mr, Lyell has offered another solution of the problem, depending 

 not on celestial but terrestrial causes. The chapter that contains it 

 abounds in valuable information and ingenious reasoning ; but when 

 the author tells us that f in every country " the land has been in some 

 " parts raised, in others depressed, by which and other ceaseless changes, 

 " the configuration of the earth' s surf ace has been remodelled again and 



* The Baobab-tree of Senegal is supposed by Adanson to have attained 

 the age of 5150 years, and De Candolie attributes to the Cupressa disticha 

 of Mexico a still greater longevity. (Lyell, vol. iii. p. 99.) 



If these opinions be correct, it seems improbable that any great change 

 either of level or climate can have taken place at these spots within the 

 last 5000 years. 



f Principles of Geology, vol. i. p. 113. 



