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- 

 thinor like an ascendino^ 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 difi'used 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 diflSculty. The 

 »iew individuals must be conveyed in their adult forms ; 

 their numbers are, in comparison, utterly insignificant ; 

 they live on land, and are 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 

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

 of a vride ocean, would fii-st give origin to unfossiliferous 

 strata ; next, to strata containing only the lowest marine 



