HIGHER LIFE UPON THE NEW CONTINENT. 363 



flourish under simple conditions of life, would be the first 

 successful immigrants ; and that more complex organisms, 

 needing for their existence the fulfilment of more complex 

 conditions, would afterwards establish themselves in some 

 thing like an ascending succession. At the one extreme 

 we see every facility. The new individuals can be con 

 veyed in the shape of minute germs ; these are infinite in 

 their numbers ; they are diffused in the sea ; they are per 

 petually being carried in all directions to great distances 

 by ocean-currents ; they can survive such long journeys 

 unharmed ; they can find nutriment wherever they arrive ; 

 and the resulting organisms can multiply asexually with 

 great rapidity. 



At the other extreme, we see every difficulty. The 

 ew individuals must be conveyed in their adult forms ; 

 their numbers are, in comparison, utterly insignificant ; 

 they live on land, and arc very unlikely to be carried out 

 to sea ; when so carried, the chances are immense against 

 their escape from drowning, starvation, or death by cold ; 

 if they survive the transit, they must have a pre-existing 

 Flora or Fauna to supply their special food ; they require, 

 also, the fulfilment of various other physical conditions; 

 and unless at least two individuals of different sexes are 

 safely landed, the race cannot be established. Manifestly, 

 then, the immigration of each successively higher order of 

 organisms, having, from one or other additional condition 

 to be fulfilled, an enormously-increased probability against 

 it, would naturally be separated from the immigration of a 

 lower order by some period like a geologic epoch. 



And thus the successive sedimentary deposits formed 

 while this new continent was undergoing gradual elevation, 

 would seem to furnish clear evidence of a general progress 

 ia the forms of life. That lands thus raised up in the midst 

 of a wide ocean, would first ffive origin to uufossiliferous 



/ o o 



strata ; next, to strata containing only the lowest marine 



