LARAMIE FLORA OF THE DENVER BASIN. 



the description of new species of invertebrates 

 it contains (p. 405) a geologic section under 

 the heading "Section of the members of 

 the Cretaceous formation as observed on the 

 Missouri River and thence westward to the 

 Mauvaises Terres." The stratigraphic units 

 of this section, which practically correspond 

 to those accepted at the present day, were 

 numbered in ascending order from 1 to 5, 

 but they were not then named. Above the Cre- 

 taceous portion of the section was recorded 

 the Eocene Tertiary, which was given a 

 maximum thickness of 250 feet. 



In 1856 the elaboration of the invertebrates 

 was continued by Meek and Hayden, 8 who 

 quoted the geologic section from Hall and 

 Meek without change, except that the Tertiary 

 was given a thickness of 400 to 600 feet and 

 was said to be composed of "beds of clay, 

 sandstone, lignite, etc., containing remains of 

 vertebrates and in places vast numbers of 

 plants, with land, fresh-water, and sometimes 

 marine or estuary Mollusca." As regards the 

 Cretaceous portion of the section they stated: 



It is worthy of note that some of the species contained 

 in the collection from the most recent Cretaceous beds of 

 the upper Missouri country appear referable to genera 

 which, according to high European authority, date no 

 further back than the true chalk, while many of them are 

 closely analogous to Tertiary forms — so close, indeed, 

 that had they not been found associated in the same bed 

 with Ammonites, Scaphitez, and other genera everywhere 

 regarded as having become extinct at the close of the 

 Cretaceous epoch, one would have considered them Tertiary 

 species. 



On subsequent pages in the same journal 

 Leidy " began the publication of the results of 

 his study of the vertebrate remains from*the 

 Judith River badlands. He did not discuss the 

 age of the beds, but in the description of the 

 final species, which was named in honor of 

 the collector, he said: "This species is named 

 in honor of Dr. Hayden * * * and which 

 remains, I suspect, indicate the existence of a 

 formation like that of the Wealden of Europe." 10 



» Meek, F. B., and Hayden, F. V., Description of new species of gastro- 

 pods from the Cretaceous formation of Nebraska Territory: Acad. Nat. 

 Sci. Philadelphia Pro?., vol. 8, p. 63, 1856. 



9 Leidy, Joseph, Notice of extinct reptiles and fishes, discovered by 

 Dr. F. V. Hayden in the badlands of the Judith River, Nebraska Terri- 

 tory: Acad. Nat. Sci. Philadelphia Proc, vol. 8, p. 72, 1856. 



io This is the beginning of the so-called Judith River problem, which 

 is considered on pp. 77-78 of the present paper. 



In their second paper u Meek and Hayden 

 took up the invertebrates that were believed 

 to be of Tertiary age and incidentally briefly , 

 described the lithology and areal extent of the 

 great lignite-bearing formation ( = Fort Union) 

 of the region as then known to them. They 

 showed that it occupies a vast area, "chiefly 

 between the forty-sixth and forty-ninth paral- 

 lels of north latitude and the one hundredth 

 and one hundred and eighth degrees of longi- 

 tude." As their adumbrations, even in this 

 first venture, regarding the age of this lignite- 

 bearing formation are so nearly in accord with 

 the modern interpretation, it may be of interest 

 to quote their statement (p. 113) in full: 



Although there can be no doubt that these deposits hold 

 a rather low position in the Tertiary system, we have as 

 yet been able to arrive at no very definite conclusion as 

 to their exact synchronism with any particular minor sub- 

 division of the Tertiary, not having been able to identify 

 any of the Mollusca found in them with those of any well- 

 marked geological horizon in other countries. Their 

 general resemblance to the fossils of the WoolricH and 

 Reading series of English geologists, as well as to those of 

 the great Lignite formations of the southeast of France, 

 would seem to point to the lower Eocene as their position. 



In the following year, however, Hayden ap- 

 pears to have modified his opinion regarding 

 the age of the lignite-bearing formations, for in 

 a short paper 12 accompanying a colored geo- 

 logic map of the country bordering Missouri 

 River, he said, in discussing the "Great Lignite 

 deposit)": 



The collections of fossils now obtained show most con- 

 clusively that it possesses the mixed character of a fresh- 

 water and estuary deposit and that it can not be older 

 than the Miocene period. It is composed mostly of clays, 

 sands, sandstones, and lignites and has yielded numerous 

 animal as well as vegetable fossils of great perfection and 

 beauty. It is chiefly remarkable, however, for the evi- 

 dence that it reveals to us of the variety and luxuriance of 

 the flora of that period. i 



In a paper immediately following that one 

 Meek and Hayden 13 continued the description 



" Meek, F. B., and Hayden, F. V., Descriptions of new species of 

 Acephala and Gastropoda from the Tertiary formations of Nebraska 

 Territory, with some general remarks on the geology of the country 

 about the source of the Missouri River: Acad. Nat. Sci. Philadelphia 

 Proc, vol. 8, p. Ill, 1856. 



i! Hayden, F. V., Notes explanatory of a map and section illustrating 

 the geologic structure of the country bordering on the Missouri River, 

 from the mouth of Platte River to Fort Benton: Acad. Nat.» Sci. Phila- 

 delphia Proc, vol. 9, p. 109, 1857. 



>» Meek, F. B., and Hayden, F. V., Description of new species and 

 genera of fossils collected by Dr. F. V. Hayden in Nebraska Territory, 

 etc.: Acad. Nat. Sci. Philadelphia Proc, vol. 9, p. 117, 1857. 



