290 THE ORIGIN OF THE OLDEST FOSSILS, ETC. 



tal, for we are told by Walcott that " one of the most important 

 conclusions is that the fauna of the lower Cambrian lived on the 

 eastern and western shores of a continent that in its general con- 

 figuration outlines the American continent of to-day." " Strictly 

 speaking, the fauna did not live upon the outer shore facing the 

 ocean, but on the shores of interior seas, straits, or lagoons that 

 occupied the intervals between the several ridges that ran from the 

 central platform east and west of the main continental land surface 

 of the time." 



This fauna was rich and varied, but it was not self-supporting, 

 for no fossil plants are found, and the primary food supply was 

 pelagic. Animals adapted for a rapacious life, such as the ptero- 

 pods, were abundant, and prove the existence of a rich supply of 

 pelagic animals. All the forms known from the fossils are either 

 carnivorous — like the medusae, corals, Crustacea, and trilobites — or 

 they are adapted — like the sponges, brachiopods, and lamelli- 

 branchs — for straining minute organisms out of the water, or for 

 gathering those which rain down from above, and the conditions 

 under which they lived were very similar to those on the bottom 

 at the present day. 



Walcott's studies show that the earliest known fauna had the 

 following characteristics : — It consisted, so far as the record shows, 

 of animals alone, and these were dependent upon the pelagic food 

 supply for support. While small in comparison with many modern 

 animals, they were gigantic compared with primitive pelagic ani- 

 mals. The species were few, but they represent a very wide range 

 of types. All these types have modern representatives, and most 

 of the modern types are represented in the lower Cambrian. 

 Their home was not the bottom of the deep ocean, but the shores 

 of a continent under water of considerable depth. 



The Cambrian fauna is usually regarded as a half-way station in 

 a series of animal forms which stretches backwards into the past for 

 an immeasurable period, and it is even stated that the history of life 

 before the Cambrian is longer by many fold than its history since. 



So far as this opinion rests on the diversity of types in Cambrian 

 times, it has no good basis ; for if the views here advocated are 

 correct, the evolution of the ancestral stems took place at the 

 surface, and all the conditions necessary for the rapid production 



