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 22 /o/o. 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, 
