THE GREEN EIVER COAL BASIK 461 



casts of bivalve shells, in sandstone, and consequently not in a good condition 

 for satisfactory determination. Indeed, in many cases, they cannot be referred 

 with confidence even to the proper genera, as none of the specimens show 

 the hinge or internal characters. So far as I have yet been able to deter- 

 mine, they seem to be mainly undescribed species. Taken collectively, as a 

 group, they present much the general fades of the fauna of the upper mem- 

 bers of the series in California referred by Professor Whitney and Mr. Gabb 

 to the Cretaceous epoch. Yet, after a careful comparison with the figures 

 and descriptions given in the California reports, I am not quite sur6 that any 

 of them are really identical with those of the Pacific slope. Nor am I entirely 

 satisfied that any of them are identical with any of the forms hitherto brought 

 from the Upper Missouri country, though some of them may possibly be found 

 to be the same as some of the neglected and. undeterminable casts we have 

 had from the upper branches of the Missouri.^ 



With the exception of the genus Inoceramus^ which is certainly repre- 

 sented by two or three species, and perhaps Anchura, all of these fossils, so 

 far as their characters can be made out, appear to be just such forms as 

 might be referred with about as much propriety to the Tertiary as to the 

 Cretaceous. In fact, it is probable, from the general absence of character- 

 istic Cretaceous types among them, (with the exceptions mentioned) that, 

 if submitted to almost any paleontologist, not aware of the fact that the 

 specimens oi Inoceramus and Anchura? occurred in the same beds, the whole 

 would be unhesitatingly referred to the Tertiary. The presence of two or 

 three species oi Inoceramus, however, and one of Anchura?, both of which, I 

 believe, are generally regarded as having become extinct at the close of the 

 Cretaceous epoch, taken in connection with the fact that these fossils are all 

 marine types, while we have, up to this time, no evidence of the existence of 

 any strictly marine Tertiary deposits in this central region of the continent, 

 would certainly favor the conclusion that these beds belong to the Cretaceous. 



From all the facts now known, I can therefore scarcely doubt that you 

 are right in referring these beds to the Cretaceous. Indeed I had arrived at 

 the same conclusion in regard to this formation, in 1860, from examining 



^ As elsewhere stated, one oyster brouglit from this formation by Colonel Simpson 

 seems to be the same as an Upper Missouri species. 



