78 THE HABITAT OF THE EURYPTERIDA 



Marine Deposits and Faunas. Sediments which accumulated 

 in the open marine waters at all times, subsequent at least to the Pre- 

 Cambric, have been found to contain a rich and varied fauna in which 

 were represented all of the larger groups of the invertebrate animal 

 kingdom which are recognized today. One need only mention the 

 prolific faunas of the Cambric of St. John, New Brunswick, and of 

 British Columbia, the Trenton of New York, the Niagaran of New 

 York and elsewhere, the Hamilton of the eastern United States, the 

 Muschelkalk and Upper Jura of Germany, the Upper Cretacic of the 

 middle and north of Europe, and the Eocenic of France and England. 

 Not only is the number of individual fossils great, represented by 

 many species, but these species are scattered through many phyla, 

 just as at the present time the organisms in the oceans are numerous 

 and diversified, no one class reigning to the complete exclusion of 

 others. This does not mean that we shall find the same distribution 

 according to phyla in the past, but we do know that it will be diverse. 

 The vertebrates, for instance, cannot be of importance in faunas 

 until their evolution has had time to take place, and thus they are 

 not found represented in the rocks in abundance before the Devonic. 

 Thus the important phylum of Pisces find no, or only rare represen- 

 tation in the early Palaeozoic rocks; but, on the other hand, there 

 were the Crustacea throughout the Palaeozoic, especially the trilo- 

 bites, which became extinct at the end of that period. And so 

 one might nicely appose the phyla, or more often orders or families, 

 which were represented in the past, but are not now, and in this way 

 we would see that the past, though different from, was similar to the 

 present, and that Palaeozoic seas, even the earliest ones, lacked not 

 in life and in the diversity thereof. 



The very nature of marine waters, their continuity and great 

 extent, suggests migration and wide distribution through currents. 

 Barriers there were, of course, both by land masses and ocean cur- 

 rents, streams of cold water, and so forth, but, nevertheless, we know 

 that migration along the coasts of the continents took place as it 

 does today and that many species or at least genera spread through- 

 out all of the oceans, for if we did not believe in the forces of migra- 

 tion and dispersal we would not have laid down the laws of correla- 

 tion which are universally recognized. In no way, then, can a typi- 

 cal marine fauna remain bottled up in one place, with none of its 

 members escaping to adjacent waters; such a thing cannot happen 

 today and it is not reasonable to suppose that it happened in any 

 geological period in the past. 



