Elevation and Subsidence of the Surface of the Earth. 409 



the total rise of the arch was about 4100 feet, while its breadth 

 from Loudon to some point in the English Channel may be 

 taken at 100 miles. If now we turn to the Table, we find, by 

 interpolation, that a thickness of 3400 feet implies a rise in 

 temperature of 68°, which, acting over a breadth of 100 miles, 

 would cause an elevation of about 4650 feet. An ample margin 

 is therefore allowed for the check to the upward movement of the 

 isogeothermals caused by denudation after emerging from the 

 sea. The lower beds being more highly heated than the upper 

 chalk, would expand more and give rise to those minor folds, or 

 " lines of elevation,''^ described by Mr. Hopkins. 



Another illustration may be desirable. Daring the early 

 eocene period an extensive ocean existed from Spain and Morocco 

 eastward through Switzerland, North Africa, Turkey, Asia Minor, 

 Persia, and Northern India to China ; and in this ocean the num- 

 mulitic limestone, some 8000 feet thick, was deposited. Here, 

 therefore, if there is any truth in the theory that thick and ex- 

 tensive limestone deposits cause elevation, we ought to find 

 marked evidence of it ; and accordingly in the Atlas, Pyrenees, 

 Alps, Apennines, Carpathians, Persian mountains, and Hima- 

 laya, all of which have been elevated since the nummulitic lime- 

 stone was deposited, we see effects produced commensurate in 

 their grandeur with the extent and thickness of the formation. For 

 if the deposition of the nummulitic limestone and the overlying 

 deposits was not the cause of the elevation of these mountain- 

 ranges, we have to seek for some other cause acting over exactly 

 the same area at the same or nearly the same time, and yet, if 

 each chain had its own independent origin, acting in different 

 directions. It certainly seems to me far more reasonable to view 

 them simply as wrinkles in the limestone caused by its expan- 

 sion ; for it must be remembered that by this theory mountain- 

 chains would be formed at those places where the deposits were 

 thickest, so that they might take various directions although all 

 formed at the same time. It is also remarkable that the highest 

 mountains, although situated in various parts of the world, have 

 all risen to about the same height (8000 feet) above the snow- 

 line. This, although difficult to account for in any other way, 

 is readily explained by supposing that the cold of the upper 

 regions has stopped their growth by preventing the further out- 

 ward movement of the isogeothermals. In this way perhaps we 

 may account for the Himalaya being higher than the Alps, with- 

 out having to suppose that the nummulitic formation was thicker 

 in India than in Switzerland. 



I have already pointed out that an alteration in the mean 

 temperature of the surface will produce the same effects as the 

 deposition or removal of matter ; and in this way many of the 



