28 Poulett'Scrope — On Mallet's Theory of Volcanic Energy. 



elevation of ridges beneath it, and throw the whole disturbance into 

 the region just outside its boundary," 



11. I have pointed out in my previous papers on this subject that 

 mountains are formed on two different plans : the one associated 

 with volcanic rocks, the other with the crystalline schists ; but the 

 Contraction theory supposes that all mountains are identically formed. 



12. My last objection to the Contraction theory is that it makes no 

 provision for tension in rocks, although faults prove tension just as 

 surely as contortions prove compression. 



I am, therefore, of opinion that the effects on the crust of the earth 

 caused by contraction have been very small, and that these effects 

 have been totally obliterated by the much larger effects caused by 

 deposition. 



In conclusion, I wish to explain that I do not consider it necessary 

 that the whole of an area should have been under water in order 

 that it may be raised by the deposition of limestone ; for, owing to 

 the lateral conduction of heat, one or more mountain ranges might 

 project out of it as islands. Indeed, I believe that all high mountain 

 ranges are the result of several subsidences and elevations, during 

 which they may never have totally disappeared under the ocean. 



Vin. — Observations on Me. Eobekt Mallet's Paper on Volcanic 

 Energy in the Philosophical Transactions for 1873, 

 PAGE 147. 



By G. PoTJLETT ScKOPE, F.R.S., F.G.S. 



WHILE giving ample credit to Mr. E. Mallet for the ingenuity 

 displayed in his novel suggestion as to the cause of volcanic 

 energy (or Vulcanicity, as he calls it), and for the elaborate experi- 

 ments and calculations which he brings to its support. Geologists 

 have some reason to complain of the supercilious tone in which he 

 notices, only to throw them aside as unworthy of notice, the theories 

 of all preceding writers on the same subject, who have expressed 

 views differing from that which he adopts. It is needless to give 

 instances of this tone which pervades the whole paper, and must 

 strike every one who reads it. 



It is, however, more important to consider — ^not the manner in 

 which Mr. Mallet's theory is brought forward — but the truth and 

 soundness of the arguments adduced by him in its favour. And for 

 this purpose we shall endeavour to examine impartially some at 

 least of the points it contains that bear on the geology of the 

 question. 



Mr. Mallet adopts the same view of the force which has produced 

 the elevations and depressions of the surface-rocks of the globe, 

 with their wrinkled foldings and frequent fractures, as MM. Cordier, 

 Dana, Constant Prevost, Elie de Beaumont, 0. Fisher, and many 

 other speculators in geological dynamics, viz. the tangential pressure 

 to which they are supposed to have been subjected under the influ- 

 ence of gravitation by the shrinkage and consequent subsidence of 

 an internal heated and slowly cooling nucleus. I do not here pro- 



