Bev. 0. Fisher — On the Formation of Mountains. 251 



Let us now consider -what would be likely to take place under the 

 conditions supposed. If 10,000 feet of deposit were laid down, and 

 the underlying rocks raised in temperature thereby 200°, they would 

 expand by 200 x 0-000005 of their previous linear dimensions ; that 

 is to say, a cubic foot of rock would, if free, have each of its faces 

 removed further from the opposite one by 0-012 of an inch, which 

 is about double the thickness of a sheet of stout writing-paper. Such 

 is the amount of expansion relied upon to produce the considerable 

 elevations given in the fourth column of the table, and which no 

 doubt it would produce, were the rocks absolutely rigid, and were 

 they to be elevated by the said expansion into a circular arch ; to 

 both of which positions I demur. Now, fixing our thoughts upon 

 such a cube of one foot of rock, it certainly seems probable that, 

 under great horizontal pressure, it would undergo the small amount 

 of compression indicated by this computation, and not expand at all 

 horizontally, but simply become about one-hundredth of an inch 

 higher. Or else the whole expansion would take place in the 

 vertical, the block suffering slight deformation and becoming about 

 three-hundredths of an inch higher than it was originally. Far 

 greater deformation than this has accompanied slaty cleavage. 



Such reasoning would lead one to doubt elevation of the kind sup- 

 posed by Capt. Hutton bein^ produced at all by such a small 

 amount of expansion. For it must be recollected that the pressure 

 caused by the expansion is horizontal, or very nearly so, and I have 

 already explained that there is really no vertical pressure from below, 

 except what just supports the rocks in their normal position. If the 

 process I have last described actually went on, then we should get over 

 the whole area an equable elevation of 3 X 0.000005 X ^ X thicTcness 

 of rocTc whose temperature is raised f} To how great a depth that 

 rise of temperature would happen, I think we cannot tell. But 

 conduction would probably equalize the temperature to that due to 

 the general level, long before any great depth was reached. And we must 

 recollect that the heat, which goes to raise the temperature of the 

 expanded layer, is abstracted from the layers underneath it, so that 

 contraction in these will accompany the assumed expansion of those. 



We have hitherto considered that the expansion of a layer of rock 

 would not disturb its position, but produce only an increase of its 

 thickness in a vertical direction. But since it is evident that in 

 nature elevation has in most instances been caused by lateral com- 

 pression, I will endeavour to estimate, in a general way, some of the 

 effects it may be expected to produce, and then apply them to test 

 Capt. Hutton's theory, and also to explain, as far as I can, one or 

 two of the observed phenomena of mountain regions. 



For this purpose we will consider that from some cause a layer 

 of rock becomes relatively larger than it was originally ; either by 



1 Mr. Batbage, Journ. Geol. Soc, vol. iii., p. 204, entirely neglects the horizontal 

 expansion, and takes account only of the vertical part, so that the elevation I have 

 given in the text is three times as great as he would have reckoned it. As a homely 

 instance of the effect I suppose, may be takea the case (jf a loaf of light bread baked 

 in a "tin." 



