434 Darwin, and after Darwin. 
which has to be met, and it can only be met by the con- 
siderations which have been advanced by Lyell and Darwin. 
The former says :— 
The total absence of any trace of fossils has inclined many 
geologists to attribute the origin of the most ancient strata to 
an azoic period, or one antecedent to the existence of organic 
beings. Admitting, they say, the obliteration, in some cases, of 
fossils by plutonic action, we might still expect that traces of 
them would oftener be found in certain ancient systems of slate, 
which can scarcely be said to have assumed a crystalline structure. 
But in urging this argument it seems to be forgotten that there 
are stratified formations of enormous thickness, and of various 
ages, some of them even of tertiary date, and which we know 
were formed after the earth had become the abode of living 
creatures, which are, nevertheless, in some districts, entirely 
destitute of all vestiges of organic bodies '. 
He then proceeds to mention sundry causes (in addition to 
plutonic action) which are adequate to destroy the fossiliferous 
contents of stratified rocks, and to show that these may well 
have produced enormous destruction of organic remains in 
these oldest of known formations. 
Darwin’s view is that, during the vast ages of time 
now under consideration, it is probable that the distribution 
of sea and land over the earth’s surface has not been uni- 
formly the same, even as regards oceans and continents. 
Now, if this were the case, “it might well happen that strata 
which had subsided some miles nearer to the centre of the 
earth, and which had been pressed on by an enormous 
weight of superincumbent water, might have undergone far 
more metamorphic action than strata which have always 
remained nearer to the surface. The immense areas in 
some parts of the world, for instance in South America, 
of naked metamorphic rocks, which must have been heated 
under great pressure, have always seemed to me to require 
! Elements of Geology, p. 587. 
