CONTEMPORARIES OF EOZOON 



195 



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imperfect indication of the fauna of its time. A 

 dredger who should have no other information as to 

 the existing population of the world, except what he 

 could gather from the deposits formed under several 

 hundred fathoms of water, would necessarily have 

 very inadequate conceptions of the matter. In like 

 manner a geologist who should have no other infor- 

 mation as to the animal life of the Mesozoic ages 

 than that furnished by some of the thick beds of 

 white chalk, might imagine that he had reached a 

 period when the simplest kinds of protozoa pre- 

 dominated over all other forms of life ; but this 

 impression would at once be corrected by the ex- 

 amination of other deposits of the same age : so our 

 inferences as to the life of the Laurentian from the 

 contents of its oceanic limestones may be very im- 

 perfect, and it may yet yield other and various fossils. 

 Its possibilities are, however, limited by the fact that 

 before we reach this great depth in the earth's crust, 

 we have already left behind in much newer for- 

 mations all traces of animal life except a few of the 

 lower forms of aquatic invertebrates ; so that we are 

 not surprised to find only a limited number of living 

 things, and those of very low type. Do we then 

 know in the Laurentian even a few distinct species, 



