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huge terrapins crawl upon its beaches, and the jungles along its 

 shores are peopled by a strange fauna, of which the dinosaurs are 

 chief. 



At the close of the Laramie period, there were such movements of 

 the earth's crust as to change to dry land the greater part of the 

 bottom of the Laramie sea, and the remainder was occupied by 

 large bodies of water, greatly larger than our present great lakes, 

 which then became wholly fresh, and so continued through a large 

 part of the Tertiary period. It is in the deposits which those great 

 fresh-water lakes have left that have been found the remains of the 

 wonderful mammalian faunas, which have become so celebrated in 

 North American geology. Other faunas, equally wonderful, have 

 probably existed elsewhere, which have shared the fate that is now 

 overtaking the buffalo, and that might have overtaken those Ter 

 tiary animals also, were it not for the very favorable conditions for 

 entombment of their remains, which the sediments of those lakes 

 afforded. 



Up to the close of the Laramie period, through the whole of 

 which a large dinosaurian fauna was continued, and in the strata of 

 which there is a commingling of Cretaceous and Tertiary types, we 

 have no evidence, in the shape of fossil remains, of the existence of 

 any mammals except about a dozen small marsupials. The Eocene 

 Tertiary strata, which rests directly upon those of the Laramie 

 group, contain the remains of a mammalian fauna, which, for mag 

 nitude, diversity, and high organization combined, has never been 

 excelled upon the earth. Nevertheless, we know nothing of the 

 ancestry of this great fauna, so far as fossil remains are concerned, 

 although the geological series of the preceding formations is quite 

 complete ; and those formations have been carefully searched for 

 such remains. The dinosaurian fauna of the Laramie period seems 

 to have ceased as suddenly as the mammalian fauna was introduced. 



Since faunas have originated under favoring, and become extinct 

 under adverse, conditions, the subject of the extinction of faunas 



is quite separate from that of their origination, although they are 

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