by Sedimentary Loading and Recurrent Expansion. 491 



raised in temperature over 1000° Fahr., and eventually the 

 whole of the underlying rocks of the earth's crust even below 

 the shell of greatest change will be proportionately affected. 

 The 10 miles of overlying sediments under such conditions 

 would be raised 1000° Fahr. at the base ; diminishing to zero 

 at the surface. 



Effects of the Rise of Temperature on the Foundation Rocks. 

 Initial Stage. 



The section of the crust of the Earth weighted and heated 

 at the same time will be subjected to a gradually increasing 

 compressive stress. So long as the actual expansive force of 

 the heated crust is insufficient to raise the weight of sediment 

 being piled upon it, it will continue to sink, though subject 

 to vertical pulsations of level due to other causes, which it is 

 not my object to treat of here. But there will eventually 

 come a time when the accumulated stresses of the expanding 

 rocks will overcome the weight of sediment, and then the 

 upheaval, folding, and building of the mountain-chain will 

 begin. But it is not to be supposed that the rise of tempera- 

 ture takes place with the mathematical precision described 

 here for mere purposes of explanation *. I have shown that 

 volcanic action often contributes to the foundation materials 

 of a mountain-range, and that intrusive sheets and dykes 

 penetrate the sediments, and ash-beds are laid down before 

 the initial movement ushering in the birth of the range takes 

 place. It is evident from this that there will be great varia- 

 tions of temperature taking place in the foundation crust and 

 the sediments during their laying down. 



The whole series of rocks, volcanic and sedimentary, will 



* This seems a fruitful source of difficulty with some minds, beginning 

 with Hopkins and ending- with Hutton, Fisher, and Middlemi.s^. Their 

 position seems to be this : if the rise of the isogeotherms into the now de- 

 posits eventually wrinkles and lifts them, why does it not begin at once P 

 Why, for instance, should not 100 feet in thickness cause a rise, and if it 

 does, how can thick beds ever be deposited ? But there are thick beds, 

 so the alleged primum mobile never acts. Q.E.D. 



After making, as I fondly thought, full explanation of the modus 

 operandi, I never anticipated the establishment of what a sense of humour 

 compels me to call another pons asinorum. Even supposing the isogeo- 

 therms rose as rapidly as the deposits were laid down, the deposits could 

 not be lifted until sufficient force accumulated to overcome the gravita- 

 tion. But in a sinking area, as I have pointed out, if there be anything 

 in the principle invoked, the presumption is that the isogeotherms are 

 in process of sinking also, and it may take a lengthened period of sedi- 

 mentation before they begin as a series to move upwards. 



There are many other possible conditioning causes. A practical 

 mechanical mind should soon see through this imaginary difficulty. 



