EARTH-LIFE GENERATION. 397 



give, but only the organic part, and not all of 

 that. The earliest organisms have hardly left 

 their trace. 



It was an epoch-making scientific act when 

 this idea of ordering the Earth's successive 

 layers through their fossils first began to 

 dawn upon a human brain, and to be applied 

 even to a limited territory. The English 

 claim in the present case the right of priority 

 for William Smith (1769-1839), a surveyor, 

 who, in pursuit of his calling was led to 

 observe the recurring kinds of fossils in 

 strata at different places. Such strata 

 he accordingly sychronized, making them 

 products of the same geologic epoch. What 

 he did for a part of England is now 

 being done for the whole Earth. He also 

 applied the basic principle of the Earth's 

 evolution that in a succession of strata 

 the oldest is found at the bottom. Thus 

 the Earth is conceived to grow by adding 

 layer to layer, like a Plant, round an unstrati- 

 fied kernel which is without fossils (azoic). 

 From this point of view Earth-life may be 

 compared to a gigantic tree with its manifold 

 concentric layers, which are continually add- 

 ed on the outside, if not year by year, at 

 least epoch by epoch. How many such layers 

 this Earth-tree (the real Yggdrasil) will de- 

 posit belongs of course to the future; but we 



