202 THE OCEAN. [Book IX. 



the granite upwards, but by the pressure of the 

 stratified surface downwards. As long as the strati- 

 fied surface remains unbroken, it is in a great 

 measure self-supporting, resisting the power of 

 gravitation, to which it gradually is compelled to 

 yield by bending, until at length it breaks. When 

 once the breakage occurs, the adjacent parts, no 

 longer offering the previous resistance to gravita- 

 tion, are drawn inwards, pressing upon the liquid 

 granite below, and forcing it outwards through the 

 fissure. Now, if we suppose two great breakages 

 to have been caused by the force of lateral pres- 

 sure, the one corresponding with the course of the 

 Rocky Mountains, the other with that of the Sierra 

 Nevada of California, it is obvious that the inter- 

 vening portion of the earth's surface, having up to 

 the time of the breakage been in a great measure 

 supported laterally, will, after its occurrence, exert 

 an increased pressure inwards proportionate to the 

 loss of lateral support ; and this inward pressure, 

 acting upon matter in a fluid or semi-fluid state, 

 will, to a greater or lesser extent, force that fluid 

 matter upwards, through the breakages ; so that 

 the unstratified rock would appear in ridges along 

 the course of each breakage. Looking at the Yo- 

 semite valley in the Sierra Nevada, a superficial 

 glance makes it appear probable that, after a granite 

 district having been formed here in the manner just 

 suggested, the bending of the surface caused by 



