HuTTON. — On the Formation of Mountains. xxxi 



also more than sufficient to elevate into the air the most towering peaks of 

 the Himalaya. 



I might also adduce the Appalachian mountains in America as a beautiful 

 illustration of the theory, every elevation that has taken place distinctly 

 following the deposition of limestone, and occurring only where the limestone 

 was deposited, except, perhaps, the last elevation after the carboniferous 

 period, which at present I cannot account for — for, according to American 

 geologists, the carboniferous limestone never overlaid these mountains. But, 

 besides the deposition of matter, any other cause that changed the temperature 

 of the surface, would also produce alterations of level — a rise in the tempera- 

 ture being followed by elevation, and a fall by subsidence owing to the cooling 

 and contracting rocks forming part of the surface of a sphere. In this way, 

 the Gulf Stream, by raising the temperature of Norway and Sweden, is 

 causing them to rise j while the cold Arctic current, sweeping down through 

 Baffins' Bay and striking against Greenland, is causing that country to 

 sink. 



Turning now to the second cause of the subversion of equilibrium, viz., 

 change in the incidence of pressure, we find our data not so satisfactory, for 

 we have no means of estimating the rigidity of the crust, and therefore of 

 the weight it would bear before beginning to move, but nearly all geologists 

 agree that most thick formations of sandstones and clays have been deposited 

 upon a sinking area, and that in a large number of cases the subsidence has 

 been approximately equal in rapidity to deposition. Now the chances are, of 

 course, enormously against subsidence being equal to deposition, unless one is 

 caused by the other, and when many cases of the kind are brought forward, 

 our former suspicion becomes almost a certainty. This, of course, only applies 

 to clays and sandstones, for I have already shown that limestones, as soon as 

 they begin to expand by heat, rise up and relieve the pressure ; but with 

 unconsolidated beds, like clay or sand, the horizontal thrust could never get 

 powerful enough to overcome the rigidity of the crust, and consequently they 

 could never rise. 



As large deposits of limestone, therefore, elevate areas, so large deposits of 

 argillaceous strata depress them. But while argillaceous strata are being 

 formed they will not only be compressed by the sinking of the spherical surface 

 on which they rest, but they will also at the same time be expanded by heat, 

 and these two, together, will throw the beds into folds or contortions. 



If we suppose that the subsidence is equal to the thickness of the formation, 

 which is the most reasonable supposition that we can make, we can calculate 

 the amount of compression due to sinking, and to expansion from heat, due to 

 different thicknesses. Some of these are given in the following table, the 



