154 GEOLOGICAL SURVEY OF THE TERRITORIES. 



apply also to the smaller ? He says also that paleontology confirms 

 Hayden's conclusion that there is no evidence of any catastrophe suffi- 

 cient to account for any sudden and complete destruction of life. The 

 change from marine waters to fresh water accounts for the destruction 

 of the marine invertebrate life, but, as Hay den* says, "the vertebrates 

 of the Lignitic period having great powers of locomotion, and being able 

 to live on laud as well as in the lakes and marshes of that time, and as we 

 have shown that there was at no time any important catastrophe or phys- 

 ical changes sufficient to affect them, could well have prolonged their exist- 

 ence far up into the Lignitic group, carrying with them as an inheritance 

 their Cretaceous characters." No one form of life should be taken as a basis 

 of classification. Cope's comparative list of vertebrate species,t under 

 Colorado and Dakota, includes two species of Plastomenus, a Tertiary 

 genus, although in a foot-note he says he so refers them provisionally. 

 The fauna, therefore, even according to his own list, is not exclusively 

 Cretaceous. Writing to Prof. C M. Dawson on some remains found in 

 the lower portion of the Lignitic formation on the forty-ninth parallel, 

 he says : $ " This is a characteristic collection of the reptiles of the Fort 

 Union Cretaceous, but with increased admixture of Eocene forms. Plas- 

 tomenus is an Eocene genus, but the reference of the new species to it is 

 not final. But you send two Eocene gar scales which have every ap- 

 pearance of belonging to the same formation. Will you re-examine your 

 notes to inform me whether they really belong to the same horizon as 

 the others f Dawson says :§ " The gar scales referred by Professor Cope 

 to the genus Clastes, were obtained at the very base of the Lignitic 

 formation and below the lowest lignite-bed." " Dinosaurian bones oc- 

 curred within a few feet of them." 



We have already seen that thecoal-beariugstrata at Coalville and Bear 

 River are undoubtedly Cretaceous. The only reason to be given for in- 

 cluding the different groups in one formation is the fact of the presence 

 of coal; and we might, then, include all coal-bearing strata, whether 

 Carboniferous, Triassic, Jurassic, Cretaceous, or Tertiary, in the same. In 

 this case the lignitic strata are very close together ; and in fact one im- 

 mediately succeeds the other. This is also the case at the base of the 

 Cretaceous in some places. Professor Newberry,|| referring to a bed of 

 lignite of Jurassic age in Northeastern Arizona, says: "The sandstone, 

 shales, and limestone lying above, also include many beds of lignite 

 closely resembling this, and on lithological grounds would appropriately 

 be grouped with it. lu fact they have been considered Jurassic, and the 

 only Jurassic rocks in this region, by the geologist Marcou, who claims 

 to have discovered the representative of this formation in New Mexico. 

 Unfortunately, however, for that classification, immediately over the 

 thin stratum of yellow sandstone which overlies the coal, are beds of clay 

 shale, with bands of limestone in which are unmistakable Cretaceous 

 fossils." Plants of the lignite above were dicotyledonous, while those 

 found below " are closely allied to some of those most characteristic of 

 the Jura and Upper Trias of Europe." ft The base of the Cretaceous 

 formation is therefore seen to resemble the base of the Tertiary. In 

 Eastern Colorado the upper part of the Cretaceous is destitute of coal. 

 In fact the Upper Fox Hills group is wanting in many localities, and 



* Notes on the Lignitic group of Eastern Colorado and portions of Wyoming, Bulle- 

 tin No. 5, second series, United States Geological Survey of Territories, p. 411. 

 t Report U. S. Geol. Survey of Terr., 1873, p. 433. 

 i Geol. Report Forty-ninth Parallel, p. 200." 

 $ Ibid. 



|| Ives's Colorado Expedition, Geological Report, p. 83. 

 11 Ives's Colorado Expedition, Geological Report, pp. 83, 85. 



