Rev. 0. Fisher — On the Formation of Mountains. 259 



calculated to have several important consequences. In the first place 

 it will originate a line of elevation along its shore-line or boundary, 

 by tending to bend down, or fracture, the crust there, so as to 

 present at that place inclined strata to the horizontal thrust. Secondly, 

 the thickness of the rigid crust being increased by the new deposit, 

 it would offer an impediment to the elevation of ridges beneath it, 

 and throw the whole disturbance into the region just outside its 

 boundary, in which case a little consideration will show that the 

 whole newly-covered area would have a slight relative movement 

 towards the disturbed area, and, as it were, nip it, so as to compress 

 the anticlinals about their roots. In the meanwhile, sinking on 

 account of its load of fresh deposit, the disturbed rocks would be 

 pushed relatively over towards it. And thus, I think, we may 

 account for what Mr. Medlicott notices as a general rule,^ viz. the 

 production of normal flexures, having their steeper sides towards the 

 basin of depression ; adding, " It would be valuable to know what 

 light the abstract consideration of the case could throw upon the law 

 thus indicated." 



This also serves to explain the fanshaped arrangement of strata ia 

 certain mountain ridges. 



We have from (2) 



X {a)— lie + X(5). 



So that if any depressions, however produced, occurred below the 

 datum level, the mountains would be increased by an equal amount. 

 And since it is almost certain that such depressions, if of consider- 

 able size, would have displacements corresponding to them in the 

 superheated rocks below (observing that X (a)=5' (jS), there would 

 be an additional rise of these rocks into the anticlinals. Since seas 

 must occupy depressions, this may help to explain the usual prox- 

 imity of volcanic vents to sea margins. 



We may conceive such depressions as have been spoken of, to be 

 sometimes formed by the weight of new deposits, which would then 

 occupy them ; but whether the depression of an area by the ac- 

 cumulation of fresh deposit would be compensated by an excessive 

 elevation in its neighbourhood, seems to depend upon the amount 

 of viscosity to be attributed to the superheated rocks. The more 

 fluid they are, to the greater distance would the pressure be com- 

 municated, and the less would be the effect in the immediate 

 neighbourhood, and mce versa. 



One word in defence of the theory of the elevation of mountains in 

 consequence of the secular cooling of the earth, which I am happy to 

 learn from CajDtain Hutton "is at present almost universally 

 accepted by geologists as the cause of . . . the upheaval of mountain 

 chains." He says that its effects must be completely absorbed by 

 the much larger ones which flow from his theory. 



If I have estimated the two at all justly, I have shown that the 

 reverse is the case ; for I have proved that if we suppose a stratum 

 500 miles thick, buried under 25 miles of crust, to have contracted 



' loc. cit., p. 45. 



