LOXOLOPHODON AND UINTATHERIUM. 



15 



of floods when the heavier materials were transported far into the lakes. All 

 these conditions are in striking contrast with the meteorological phenomena of 

 this desert land at the present day. 



The flora of the upper Cretaceous period in this region presents an inter- 

 esting mingling of hardy northern plants with those of a more tropical 

 character. The plants of the Laramie are well known to resemble those of the 

 European Tertiary formations It is not improbable that they survived the 

 changes accompanying the upheaval of the land and clothed the borders of 

 these lakes, although the manner of sedimentary deposition during the Bridger 

 epoch did not often admit of the preservation even of the littoral plants. 

 Here and there, however, are found the fragmentary remains of reeds and 

 other water-plants. The position of some of these is indicated in the strati- 

 graphical section accompanying this memoir. The abundance of polydactyle 

 forms, or spreading feet, among the mammals adds probability to the natural 

 supposition that the lakes were bordered by wide-stretching marshes. 



As to the causes of extinction there is much evidence to show that they 

 were slow and natural, very much such causes as we should observe on 

 the borders of similar lakes in Southern Africa or elsewhere. The manner in 

 which the parts of a skeleton are found widely scattered, the occasional evi- 

 dence from the position of the limbs in the rock that the animal has been mired, 

 the absence of large numbers of bones in any one locality, all indicate a long 

 period in which the struggle for existence was not intensified by rapid geologi- 

 cal changes. The great variety of species which succeed one another and are 

 closely allied in structure afford further proof of a long undisturbed period 

 in which these gradual modifications could arise. The prevalence of weapons 

 of defence, such as the great tusks and cranial protuberances of Loxolophodon, 

 the sharp dentition and powerful muscles of Palcsosyops, indicated by the skull, 

 the tusks of Achcenodon, and the full dental series of a primitive Rhinoceros, 

 all go to show that the greatest contest was between the animals of differ- 

 ent famines rather than against unusually violent forces of nature. 



Enough has been written to clearly introduce the short study of the 

 Dinocerata which follows. They were a class of animals which present fea- 

 tures of great interest, and so numerous and characteristic of this geological 

 period that one writer has chosen to name the whole series of Bridger rocks 

 after them. The two species which will be described represent two of the 

 principal genera of the sub-order; namely, Uintatherium and Loxolophodon. 

 No explanation is needed of the length of this geological sketch with its accom- 

 panying maps, further than to say that it is hoped it will also serve to assist 

 the understanding of some of the other Bridger Eocene fossils. 



