Appendix to Chapter V. 425 



able ages in their common work of destruction, that when 

 we try to realise what it must amount to, we can scarcely 

 fail to wonder, not that the geological record is highly im- 

 perfect, but that so much of the record has survived as we 

 find to have been the case. And, if we add to these erosive 

 and solvent agencies on land the erosive and solvent agencies 

 of the sea, we may almost begin to wonder that anything 

 deserving the name of a geological record is in existence 

 at all. 



That such estimates of the destructive powers of nature 

 are not mere matters of speculative reasoning may be amply 

 shown by stating one single fact, which, like so many others 

 where the present subject is concerned, we owe to the 

 generalizations of Darwin. Plutonic rocks, being those which 

 have emerged from subterranean heat of melting intensity, 

 must clearly at some time or another have lain beneath the 

 whole thickness of sedimentary deposits, which at that time 

 occupied any part of the earth's surface where we now find 

 the Plutonic rocks exposed to view. Or, in other words, 

 wherever we now find Plutonic rocks at the surface of the earth, 

 we must conclude that all the sedimentary rocks by which they 

 were covered when in a molten state have since been entirely 

 destroyed ; several vertical miles of the only kinds of rocks 

 in which fossils can possibly occur must in all such cases 

 have been abolished in Mo. Now, in many parts of the 

 world metamorphic rocks which have thus gradually risen 

 from Plutonic depths, while miles of various other rock- 

 formations have been removed from their now exposed 

 surfaces cover immense areas, and therefore testify by their 

 present horizontal range, no less than by their previously 

 vertical depth, to the enormous scale on which a total 

 destruction has taken place of everything that once lay 

 above them. For instance, the granitic region of Parime is 

 at least nineteen times the size of Switzerland; a similar 

 region south of the Amazon is probably larger than France, 



