wAKDl HISTORICAL RKVIEW OF OPINION. 417 



Eocene period, and existed contemporaneously with an Eocene flora, or 

 else that a tlora wonderfully prophetic of Eocene times anticipated its 

 age and flourished in the Cretaceous period to the exclusion of all Cre- 

 taceous plant forms. * * * In either case, the fact remains that 

 here the physical and other conditions were such that one of the great 

 kingdoms of life, iu its progress of development, either lost or gained 

 upon the other, thus destroying relations and associations which ex- 

 isted between them in those regions from which were derived the first 

 ideas of the life boundaries of geological time, causing here api)arent 

 anomalies." He adds the following iuipoitant paragrapli: "Much of 

 the confusion and discrepancy has, in my opinion, arisen from regard- 

 ing dift'erent horizons as one and the same thing. It must be dis- 

 tinctly understood that this group as it exists east of the mountains 

 in Colorado is very difl'erent from, and must not be confounded with, 

 the horizon in which much of the Utah and New Mexican lignite 

 occurs, and which belongs undoubtedly to the Lower Cretaceous; and, 

 further, that the extended explorations of Hayden and others would 

 seem to prove almost conclusively that the Colorado lignitic group is 

 the direct southern stratigraphical equivalent of the Fort Union group 

 of the Upper Missouri, which is considered generally to be no older 

 than the Eocene, while Newberry asserts it to be ]\Iiocene." 



Mr. Lesquereux returns again, in his contribution to this same 

 volume, to the defense of his former position. He disposes in a man- 

 ner of the statement that characteristic Cretaceous molluscan fossils 

 had been found "above the beds of the lignitic formations" by quot- 

 ing Messrs. Cox and Berthoud, the collectors of the specimens about 

 which so much had been said, who both show that the conditions under 

 which they occurred were such as to render their stratigraphical posi- 

 tion too doubtful to form the basis for such important generalizations. 

 He reasserts his belief in "the unity of the Lignitic formation in its 

 whole," and reargues the whole case. He also revises his " groups" and 

 gives lists of all the species found in each. 



In Volume VII of the Canadian Naturalist, p. 241, published in 1874, 

 Mr. George M. Dawson discusses " The Lignite Formation.- of the West," 

 now discovered to extend far up into Canadian territory. He regards 

 them as of later age than the Cretaceous and accepts the view of Messrs. 

 Hayden and Lesquereux that the Fort Union group is Eocene. Re- 

 ferring to theopinionsof Cope, he says: "The evidence does not appear 

 to show that the Cretaceous si)ecies were of themselves becoming rapidly 

 extinct, but that over the Western region, now forming part of this 

 continent, the physical conditions changing drove the Cretaceous 

 marine animals to other regions, and it is impossible at present to tell 

 how long they may have eiulured in oceanic areas iu other parts of the 

 world. This being so, and in view of the evidence of the preponderant 

 animal and vegetable forms, it seems reasonable to take th^ well marked 

 base of the Lignite series as that of the lowest Tertiary, at least at 

 G GEOL 1!7 



