218 Reiteration of the Earth. 



ing, I do not believe to be very deep-seated. These rocks I 

 put out of consideration for the present ; the remarks about to 

 be offered apply to granite and its congeners, under which head 

 I would give to every one full liberty to include or reject quartz- 

 rock, gneiss, mica-slate, eurite, cipollino, hornblende-rock, ser- 

 pentine, &c. Some or all of these, it is the boundea duty of 

 central heat to fuse and to eject. 



Such and so limited are the means of chemistry, that of many 

 substances thus brought within the sphere of our inquiries, the 

 point of fusion is at this day unascertained. The author of the 

 masterly publication before adverted to, brought together many 

 useful observations upon this subject. He observes that " La- 

 voisier could not melt a particle of carbonate of lime by the in- 

 tense heat of a burning mirror, and that quartz, according to 

 Saussure, requires for its fusion a temperature r=: 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 refractory, 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 thick- 

 ness and extent of these rocks, comprising entire mountains and 

 mountain chains), must be prodigious; 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 in- 

 convenience of this distribution becomes still more apparent, 

 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 wit)i sufficient force, in many instances, to 

 raise the bed of the sea to the height of an alpine chain. I will 

 not attempt to point out to you the way in which this is accom- 

 plished, 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 



