GEOLOGICAL SURVEY OF THE TERRITORIES. 165 



of the most valuable of the coal beds of this region, are crowded with bi- 

 valve shells, two species of which Mr. Meek has named Cyrena fraeta, and 

 C. crassatelliformis, regarding them as tertiary. They are undoubtedly 

 brackish- water forms and show a sort of middle position — that is, middle 

 or upper eocene. That there is a connection between all the coal beds 

 of the West I firmly believe, and I am convinced that in due time that 

 relation will be worked out and the links in the chain of evidence joined 

 together. That some of the older beds may be of upper cretaceous age 

 I am prepared to believe, yet until much clearer light is thrown upon 

 their origin than any we have yet secured, I shall regard them as belong- 

 ing to my transition series or beds of passage between the true creta- 

 ceous and the tertiary. When the large collections of fossil plants from 

 the West, now in the possession of Dr. Newberry, are carefully studied, 

 we shall have a much better basis upon which to rest a conclusion. It 

 will be seen at once that one of the most important problems in the geol- 

 ogy of the West awaits solution, in detecting, without a doubt, the age of 

 the coal series of the West, and the exact line of demarkation between 

 the cretaceous and tertiary periods. 



The study of this question shows the importance of the continued 

 accumulation of facts and the collection of organic remains. Neither 

 can we place too rigid reliance on the teachings of the fossils, for it has 

 already been shown many times that the fauna and flora of the tertiary 

 deposits of this country, when compared with those of the Old World, 

 reach back one epoch into the past. We have already obliterated the 

 chasm between the permian and the carboniferous era, and shown that 

 there is a well-marked inosculation of organic forms — those of supposed 

 permian affinities passing down into well-known carboniferous strata, 

 and admitted carboniferous types passing up into the permian. We 

 believe that the careful study of these transition beds is destined to oblit- 

 erate the chasm between the cretaceous and tertiary periods, and that 

 there is a passing down into the cretaceous period of tertiary forms, and 

 an extending upward into the tertiary of those of cretaceous affinities. 

 It appears also, that every distinct fauna or flora of a period ought 

 to contain within itself the evidence of its own age or time of existence, 

 with certain prophetic features which reach forward to the epoch about 

 to follow. It there is a strict uniformity in all the operations of nature 

 when taken in the aggregate, as I believe there is, then this is simply in 

 accordance with the law of progress which in the case of the physical 

 changes wrought out in the geological history of the world has operated 

 so slowly that infinite ages have been required to produce any percep- 

 tible change. The position that I have taken in all my studies in the 

 West is that all evidences of sudden or paroxysmal movements, have 

 been local and are to be investigated as such, and have had no influence 

 on the great extended movements which I have regarded as general, uni- 

 form, and slow, and the results of which have given to the West its 

 present configuration. The splendid group of fossils obtained on the 

 Upper Missouri, from the Fox Hills Group or upper cretaceous beds, 

 illustrate the prophetic element 1 have mentioned above. Among them 

 are many true cretaceous forms, as Ammonites, Baculites, Inoceramus,&c, 

 yet these all present such a modern facies that they seem plainly to look 

 forward into the succeeding epoch, which in the case of our Atlantic 

 coast was strictly marine. It was no fault of the fossils themselves that 

 they were mistaken in this instance. 



We may suppose that near the close of the cretaceous period, the 

 ocean extended all over the area west of the Mississippi, from the Arc- 

 tic Circle to the Isthmus of Darien. How much of the country east of 



