HuTTON. — On the Formation of Mountains. 287 



solid portion. This is meclianically impossible, because the resistaiice to 

 sheering would be far greater than the resistance to crushing when the area 

 exposed to the compression was small compared to the area of the surface over 

 which sliding has to take place. Neither in nature do we find any of these 

 horizontal faults, which ought to be numerous and of considerable amount if 

 the contraction theory be true. In the example, for instance, given by 

 Mr. Fisher (Trans. Cam. Phil. Soc, 1869, p. 15, fig. 3), the central portion 

 must have been faulted over the lower contracting beds'for nearly half a mile. 

 In this way utter confusion would reign in stratigraphical geology — palteozoic 

 rocks would have slipped for miles over mesozoic rocks, granite over sti-atified 

 beds, etc. It is quite certain that nothing of the kind has taken place in any 

 portion of the earth's crust that has yet been examined. It is, however, 

 accepted as probable by Professor Shaler (Geological Mag., Y., p. 511) ; and 

 Mr. Fisher also, when advocating the contraction theory, appears to see no 

 difficulty in the thrust, being extended through 50 miles of rock, although, 

 when criticising the deposition theory, he says that the thrust can only be 

 supposed to extend to an infinitesimal distance. 



2. From the absence of any weight on the compressed rocks ; from the 

 impossibility of one part slij)ping horizontally over another ; and from the 

 absence of any support if any part should rise up into an anticlinal, we may, 

 I think, confidently assert that the crust of the earth would simply crush up 

 from the efiect of contraction, and would rise uniformly over the whole sui-face. 

 Mr. Fisher's formula, therefore, for the elevation should be h — he instead of 

 h=2k')ne. 



3. If, however, it be granted — for the sake of argument — that the strata 

 did not crush, but rose up on the lines of least resistance, it seems to me that 

 these lines would take radiating directions from an area of depression ; and 

 that when these lines were once established, whatever their direction might be, 

 elevation should be continuous on them. The theory, therefore, by itself 

 appears to ofier no explanation of oscillations in level. Professor Dana, 

 however, seems to see no difficulty from this cause (Geology, 1863, p. 718, etc.), 

 but he gives no explanation of it. 



4. The same being granted as before : as the upper beds must undergo the 

 greatest compression, the foldings would commence at the surface and would be 

 propagated downwards in decreasing amoimt, and, as all sedimentary beds 

 miist once have occupied the surface, it follows that all strata should he more 

 or less folded in 2)ro2)ortion to their age, because the older they are the larger 

 must have been the proportional area originally occupied by each. But we 

 know that there are large districts in Russia and JSTorth America formed of 

 undisturbed palaeozoic rocks, while in Switzerland and Northern India tertiary 

 beds are highly contorted. 



