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dinosaurian region, as one of the results of those land movements 

 by which the Laramie sea was destroyed. 



I am well aware that this proposition is not fully established, but 

 the series of strata preceding those which contain the mammalian 

 remains is so complete as to indicate the prevalence of conditions, 

 through at least the whole of the Laramie period, which were as 

 favorable for mammalian existence as those of any subsequent 

 period. And, although that series of strata has been quite as fully 

 investigated as any other strata of the west, no trace of the ancestry 

 of the mammalian fauna referred to has been discovered. 



The immediate superposition of the remains of the mammals upon 

 those of the dinosaurs, at the junction of the two formations which 

 contain them respectively, indicates that the two mighty faunas met 

 upon the same ground, in a contest for supremacy, which was de 

 cided in favor of the mammals, and that the dinosaurs then disap 

 peared from the face of the earth. That this veritable "battle of 

 the giants ' ' was sharp and decisive, is probable, from the fact that 

 there is no such association of the remains of the two faunas as to 

 indicate that they lived together any considerable length of time. 



Other strange and interesting land faunas succeeded those mam 

 mals which have just been referred to, but time will not permit me 

 now to speak of them. I will therefore close my remarks with some 

 reference to the manner in which, as I conceive, a large part of the 

 gill-bearing fauna of the Mississippi river system has originated, 

 effected its descent to the present time, and attained its present 

 broad distribution. 



The close similarity which exists between- the molluscan fauna of 

 the Laramie group and that of the present Mississippi river system, 

 is apparent even upon casual observation. A large proportion of 

 those mollusks are not only of the same types in each fauna respec 

 tively, but it is difficult to say how some of the fossils differ specifi 

 cally from the living forms. This resemblance is strikingly ex 

 emplified among the Unionidae. Those of that family now living 

 in the Mississippi river system comprise a large variety of peculiar 



