33 2 PRE-DETERMINATION IN NATURE 



bridges do not involve want of permanence in their termini. 

 Because an engineer has bridged the Firth of Forth, it does not 

 follow that the banks of this inlet did not exist before the 

 bridge was built ; and if the bridge were to perish, the evidence 

 that trains had once passed that way would not justify the 

 belief that the bed of the Firth had been dry land, and the 

 areas north and south of it depressed. The more we consider 

 this question the more we see that the permanence, growth 

 and sculpture of the continents are parts of a great continuous 

 and far-reaching plan. This view is strengthened rather than 

 otherwise, when we consider the probable manner in which the 

 enormous weight of the continents is sustained above the 

 waters. We may attribute this, on the one hand, to rigidity and 

 lateral arching and compression, or, on the other, to what may 

 be termed flotation of the lighter parts of the crust ; and there 

 seems to be little doubt that both of these principles have been 

 employed in constructing the "pillars which support the earth." 

 It is evident, however, that an arch thrown over the internal 

 abyss of the earth, or a portion of its crust so lightened as to be 

 pressed upward by its heavier surroundings, must, when once 

 established, have become a permanent feature of the earth's 

 foundations, not to be disturbed without calamitous conse- 

 quences to its inhabitants. 



It is the part of the philosophical naturalist to bring together 

 these apparent contrarieties of mutation and permanence ; both 

 of which are included, each in its proper place, in the great 

 plan of nature. It is therefore my purpose in the present 

 chapter to direct attention to some of the terminal points or 

 fixed arrangements that we meet with in the course of the 

 geological history, and even in its earlier parts, and more par- 

 ticularly in reference to the organic world. This, which is in 

 itself constantly changing, has been placed under necessity to 

 adhere to certain determinations fixed of old, and which 

 regulate its forms and possibilities down to our own time. 



