10 



LARAMIE FLORA OF THE DENVER BASIN. 



tioned. In the same report Marvine 3e had an 

 elaborate paper on the results of his studies in 

 Middle Park, Colo., in which he considered 

 among many other things, the age of the 

 lignite-bearing formations of Colorado. After 

 alluding to the weakness of the invertebrate 

 evidence for the Cretaceous age and the ap- 

 parent strength of the evidence derived from 

 the terrestrial vertebrates, he said: 



It must be supposed, then, that either a Cretaceous 

 fauna extended forward into the Eocene period and 

 existed contemporaneously with an Eocene flora, or else 

 that a flora, wonderfully prophetic of Eocene times, antic- 

 ipated its age and flourished in the Cretaceous period to 

 the exclusion of all Cretaceous 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, in its progress of development, either lost or gained 

 upon the other, thus destroying relations and associations 

 which existed between theni in those regions from which 

 were derived the first ideas of life boundaries of geologic 

 time, causing here apparent anomalies. 



As a probable explanation of these apparent 

 discrepancies, Marvine wisely concludes as 

 follows: "Much of the confusion and discrep- 

 ancy has, in my opinion, arisen from regarding 

 different horizons as one and the same thing." 



In his report for 1873 Lesquereux had a 

 further paper on the "Lignitic" flora in which 

 he of course argued still more strongly for its 

 Tertiary age. He also revised the several 

 "groups" into which he divided the section of 

 lignite-bearing rocks and presented full lists of 

 the species of plants found in each. 



In Hayden's original description of the Fort 

 Union formation he predicted that it would be 

 found extending into Canadian territory, and 

 this prediction was verified in 1874 by George 

 M. Dawson, 37 who published an article in which 

 he accepted the views of Hayden and Les- 

 quereux and referred the Fort Union to the 

 Eocene. In discussing the views of Cope he 

 said : 



The evidence does not appear to show that the Creta- 

 ceous species 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 im- 

 possible at present to tell how long they may have en- 

 dured in oceanic areas in 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 



" Marvine, A. B., Report of the Middle Park division: U. S. Geol, 

 and Geog. Survey Terr. Ann. Rept. for 1873, p. 107, 1874. 



>' Dawson, G. M., The Lignite formations of the West: Canadian 

 Naturalist, vol. 7, p. 241, 1874. 



the well-marked base of the Lignite series as that of the 

 lowest Tertiary, at least at present. The formation de- 

 scribed belongs to this lowest Tertiary, being, in fact, an 

 extension of Hayden's Fort Union group, and from analogy 

 may be called Eocene. _, 



The work upon which Dawson's views were 

 based was done in connection with the British 

 North American Boundary Commission, of 

 which he was geologist. In a report of progress 

 for 1873, published in 1874, he affirmed his 

 original statement in the following language: 38 

 The formation is, however, undoubtedly an extension 

 of the Great Lignite or Fort Union group of strata of 

 Hayden, as developed in the Western States and Terri- 

 tories. * * * These strata immediately succeeding 

 the Cretaceous rocks are the lowest American representa- 

 tives of the Tertiary series and have been called, for this 

 reason, Eocene. 



In the final report of the Boundary Commis- 

 sion, published in 1875, the same views were 

 expressed. 



About this time John J. Stevenson, who was 

 then associated with the Wheeler Survey, 

 published a number of papers on the geology 

 of portions of Colorado and New ^ Mexico in 

 which he argued strongly for the Cretaceous 

 age of the lignite-bearing beds, especially along 

 the Front Range. In a chapter on the age of 

 the Colorado lignites 39 he reviewed the opinions 

 of Hayden, Lesquereux, and others and con- 

 cluded that the presence of the supposed 

 fucoid Hdlytnenites major was an indication 

 of Cretaceous rather than Eocene age, as 

 advocated by Lesquereux. Subsequent study 

 has shown that Stevenson was correct in 

 referring the beds containing Halymenites to 

 the Upper Cretaceous, but he failed to note 

 the presence of the profound unconformity 

 that has since been demonstrated by Whitman 

 Cross and W. T. Lee to occur in the midst of 

 this supposedly continuous coal-bearing section. 



In the annual report of the Hayden Survey 

 for 1874, published in 1876, there are three very 

 important papers dealing more or less com- 

 pletely with this subject. The first of these is 

 one by Hayden, in which he summed up his 

 understanding of the lignite group at that date. 

 He gave a brief history of the group and 

 pointed out that the evidence for its age, as 

 interpreted by different geologists and paleon- 

 tologists, is very conflicting. He said: 



88 Dawson, G. M., Report on the Tertiary Lignite formation in the 

 vicinity of the 49th parallel, British North Am. Boundary Com., 1874. 



«■ U. S. Geog. and Geol. Surveys W. 100th Mer. Rept., vol. 3, pp. 

 404-410, 1875. 



