174 LIFE ON THE EARTH. 



to be continued in the interval between the epoch 

 of Stonesfield and that of Australia, and the effects 

 summed by natural selection, the result is the modern 

 Trigonia, scarcely differing more in appearance from 

 the fossil species than they differ one from another. 



But if not so derived, by continual descent, but 

 sprung from separate contemporaneous branches of 

 one stem of life, arriving at a given standard of 

 excellence at such enormously different epochs, 

 how should it happen that Plants and, Quadrupeds 

 on land, Sharks and Mollusks in the sea, should in 

 each of these two cases pass with equal advance 

 along the streams of change, moving in one case so 

 fast, in the other so slow? But if the branches 

 sprang at different times and led to these similar 

 results, would this double origin in time, for several 

 similar forms, in similar associations, fit with the 

 hypothesis of continual development ? 



