354 THE BIOLOGY OF THE SEASONS 



is quite indiscriminate, and therefore without direct import- 

 ance in evolution. It is very important to understand 

 clearly that the only eliminative processes that can be 

 regarded as counting for much in evolution are those 

 which are discriminate and consistent. 



Another consideration of some interest is brought home 

 to us when we watch the jetsam being covered up by the 

 sand either borne in by the tide or blown by the wind. We 

 see how the first step towards fossilisation might be taken 

 when some change in currents piles up a heavy sandbank 

 near the high-tide mark, burying a sample of the jetsam. 

 But even if the sample was a good one, and if all should be 

 preserved in a future sandstone, the result would be far 

 from a fit representation of the local fauna of our times. It 

 would be almost as misleading to judge of the civilisation of 

 the early twentieth century by the debris washed up on the 

 beach near a large town. Nor should one fail to notice that 

 even if a whole stretch of jetsam were quickly buried, many 

 items would have no chance of being preserved or of being 

 well preserved, for the Amphipods and Bacteria and other 

 scavengering creatures have already begun their destructive 

 work. The sea's memoranda are apt to pass quickly beyond 

 all hope of deciphering. 



We cannot watch the jetsam through several consecutive 

 days without getting vivid illustrations of the circulation 

 of matter. The squid is scarcely dead before the gulls are 

 pecking at it, and even land birds like rooks come down to 

 the feast. The Amphipods already referred to are con- 

 tinually doing with their microscopic nibbling what birds do 

 when they pick a dead fish clean. We lift up the substantial 

 shell of an oyster or of a " roaring buckie " and find it 

 riddled with holes, neatly bored as if with a gimlet, the 

 work of a boring sponge Cliona, which thus helps the shell 

 a long way towards its incorporation with the sand. It is an 



