372 GEOLOGICAL SURVEY OF THE TEREITORIES. 



is forcibly in favor of the Tertiary age of the Lignitic. Nearly one-half 

 of the species of fossil plants found at Black Butte are identical with 

 or closely related to Eocene and Miocene species of Europe. On this 

 subject even the invertebrate animals seem to point out to the same 

 conclusions ; for Professor Meek remarks, {loc. cit, p. 460,) " that he 

 found directly associated with the reptilian remains of Black Butte 

 (that saurian imbedded in Tertiary leaves) a shell which he cannot dis- 

 tinguish from Viviparus trocMformis, originally described from the Lig- 

 nitic formations at Fort Clark, on the Upper Mississippi, a formation 

 that has always been regarded as Tertiary by all who have studied its 

 fossils, both animal and vegetable." The whole discussion on the subject, 

 continued by Professor Meek, and reviewed clearly on the following 

 pages, (pp. 461-4G2,) establish the same fact, that paleontological evi- 

 dence from remains of invertebrate animals is rather in favor of the 

 Tertiary than of the Cretaceous age of the group. 



The conclusion of Professor Cope amounts to this : that from the Da- 

 kota group to the top of roof of the Black Butte main coal he met with 

 an uninterrupted series of animal Cretaceous remains, mollusks in the 

 lower beds and vertebrates in the higher, proving that the beds are Cre- 

 taceous(!). Comparing this with the flora of the Lignitic, he concludes 

 that a Tertiary flora was contemporaneous with a Cretaceous fauna, 

 establishing an uninterrupted succession of life across what is generally 

 regarded as one of the greatest breaks in geological time. 



This conclusion does not appear to exactly conform to facts, at least 

 on the point of view of vegetable paleontology, for on this account, and 

 contrary to what is remarked by Professor Cope in following his re- 

 searches on the bones of extinct species of animals, we have from the 

 Dakota group to the lowest strata of the Lignitic, or to the same bed at 

 Black Butte, where the bones of that dinosaurian were found, an evi- 

 dent and total break in the succession of vegetable type, quite as 

 marked as it can be in passing from the Jurassic to the Cretaceous. 

 This anomaly may be explained in considerinig this fact : that the flora 

 is in direct collateral relation with atmospheric circumstances which do 

 not influence, at least not in the same way and with the same activity, 

 the marine world and the land vegetation. Morever the lower Eocene 

 of Europe has a series of clay beds bearing remains of land plants. 

 They are intermediate, it seems, between the upper Cretaceous and the 

 Lignitic formations, and thus indicate long periods of time sufficient to 

 account for great modificatiohs in the flora. 



6th. Leaving aside these considerations, which bear indirectly on the 

 subject, I have to come back to the question of the i^recedence which in 

 a case like this should be accorded to fossil plants, for the determina- 

 tion of the age of the formation ; for I cannot leave without contra- 

 diction a critical remark made against the report of last year, which, 

 among others, says : * 



Mr. Lesquereus has met the statements of Professors Meek, Cope, and Marsh, that 

 Cretaceous mollusks had been found in and overlj^iug the Colorado lignite deposits, 

 by pointing to his 250 species of fossil plants, claiming that they far outweigh the tes- 

 timony of the animal remains. In fact, however, these fossil plants have little bear- 

 ing on the question. 



The absence of fossil mollusks in the Colorado basin has been proved; 

 C>ut even admitting the contrary, and taking as an analogous case the 

 coal of Black Butte, over which the skeleton of a dinosaurian, AgatJiauma 

 sylvestrisjf has been found imbedded into leaves of Eocene plants, shall 

 we for the reason of the presence of these Cretaceous remains, still more 



* Dr. Newberry, in Journal of American Arte and Sciences, vol. vii, April, 1874, p. 403. 

 t Cope, Second Bulletin of the United States Geological Survey. 



