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 



1 Elements of Geology, p. 587. 



