The Mighty Deep 



foundation — that of a steadily cooling Earth — 

 that of a more or less heated interior, and of 

 a hardened crust. 



The cooling of the inside goes on slowly, and 

 not uniformly, since conditions differ in different 

 places. As the heated materials become cooler 

 they lessen in size. Thus the nucleus is constantly 

 getting a little too small for the inclosing crust. 



If the said crust were a solid shell, compact 

 and strong enough in all its parts to resist the 

 strain of its enormous weight, it might be ex- 

 pected to keep its shape and position unchanged, 

 holding loosely within itself the shrinking centre. 

 But it is formed of a great number of materials, 

 some hard, some soft and yielding. Therefore, 

 as the central parts lessen in size, the crust sinks 

 downwards, and in so doing it wrinkles into huge 

 folds, like the rind of a shrivelling orange or the 

 skin of a very old man's face. A ridge is 

 pushed up here ; a furrow extends there. Here 

 a long range of mountains is found ; there we 

 see a succession of valleys. 



By these movements the Ocean is both helped 

 and hindered in its ''building." As new land 

 is formed under water, the ''crust-creep" perhaps 

 raises it gently, and a strip of sea becomes dry 

 land. But another portion of the work, that 



ii8 



