THE ORIGIN OF THE OLDEST FOSSILS, ETC. 469 



long period when the bottom was uninhabited. The slow geo- 

 logical changes by which the earth gradually assumed its present 

 character present a boundless field for speculation, but there can 

 be no doubt that the surface of the primeval ocean became fit 

 for living things long before the deeper waters or the sea floor, 

 and during this period the proper conditions for the production 

 of large and complicated organisms did not exist, and even after 

 the total amount of life had become very great it must have con- 

 sisted of organisms of small size and simple structure. 



Marine life is older than terrestrial life, and as all marine life 

 has shaped itself in relation to the pelagic food supply, this itself 

 is the only form of life which is independent, and it must there- 

 fore be the oldest. There must have been a long period in pri- 

 meval times when there was a pelagic fauna and flora rich beyond 

 limit in individuals, but made up of only a few simple types. 

 During this time the pelagic ancestors of all the great groups of 

 animals were slowly evolved, as well as other forms which have 

 left no descendants. So long as life was restricted to the sur- 

 face no great or rapid advancement, through the influences which 

 now modify species, was possible, and we know of no other influ- 

 ences which might have replaced them. We are, therefore, 

 forced to believe that the differentiation and improvement of the 

 primitive flora and fauna was slow, and that, for a vast period of 

 time, life consisted of an innumerable multitude of minute and 

 simple pelagic organisms. During the time which it took to form 

 the thick beds of older sedimentary rocks, the physical con- 

 ditions of the ocean gradually took their present form, and dur- 

 ing a part at least of this period the total amount of life in the 

 ocean may have been very nearly as great as it is now without 

 leaving any permanent record of its existence, for no rapid 

 advance took place until the advantages of life on the bottom 

 were discovered. 



We must not think of the populating of the bottom as a 

 physical problem, but as discovery and colonization, very much 

 like the colonization of islands. Physical conditions for a long 

 time made it impossible, but its initiation was the result of bio- 



