r 



TWO OBJECTIONS CONSIDERED 



land animals, on the other hand, owe their oc- 

 casional preservation to the accidents of dying 

 in sheltered caves, or of being covered with 

 blown sand or peat-moss, or of being frozen in 

 Arctic ice. Trees with solid trunks, littoral and 

 marine animals, especially crustaceans and shell- 

 covered mollusks, are more likely to be pre- 

 served than other organisms. But in the second 

 place, the majority of the organisms once fos- 

 silized are afterwards destroyed along with the 

 sedimentary strata which contain them. Since 

 there have been several enormously long alter- 

 nating periods of elevation and of subsidence, 

 it follows that all the older sedimentary strata 

 must have been metamorphosed by volcanic 

 heat. These oldest rocks have sunk to a depth of 

 six or eight miles, down below the ocean-floor, 

 where they have been metamorphosed by the 

 heat of the molten liquid below, and whence they 

 have again been slowly shoved up above water- 

 level, with all traces of their organic contents 

 obliterated. This process must have occurred 

 so many times as to have destroyed all but the 

 later records of life. The title "palaeozoic,'* 

 formerly applied to the Silurian rocks, is a mis- 

 nomer. It was formerly supposed that there were 

 no fossil-bearing rocks below the Silurian. But 

 within a few years the Cambrian and Lauren- 

 tian strata have been discovered, carrying us 

 back into an antiquity nearly twice as great as 



55 



