Hurron.—On the Formation of Mountains. 287 
solid portion. This is mechanically impossible, because the resistance 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—paleozoic 
rocks would have slipped for miles over mesozoic rocks, granite over stratified 
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., V., 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 pe 
supposed to extend to an infinitesimal distance. 
2. From the absence of any weight on the compressed rocks ; from the 
impossibility of one part slipping 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 effect of contraction, and would rise uniformly over the whole surface. 
Mr. Fisher's formula, therefore, for the elevation should be h=ke instead of 
h=2kme. 
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 offer 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 amount, and, as all sedimentary beds 
must once have occupied the surface, it follows that all strata should be more 
or less folded in proportion 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 North America formed of 
undisturbed palzozoic rocks, while in Switzerland and Northern India tertiary 
beds are highly contorted. 
