Reviews — United States Geological Surveys. 415 



Lesquereux, "it is especially from our jflora of the Lower Cretaceous 

 (the Dakota group) that we have a vegetable exposition peculiarly 

 at variance with that of Europe at the same epoch, and whose types 

 so much resemble those of the European Tertiary that the evidence 

 of the age of the formation, where the plants have been found, could 

 not be admitted by palceontologists until after irrefutable proofs of 

 it had been obtained," (No. 2, p. 378.) The Dakota flora consists 

 chiefly of dicotyledonous leaves of genera to which belong most of the 

 living arborescent plants of the American continent and of its pre- 

 sent climate, as Liquidamhar, Salix, Betula, Liriodendron, Magnolia, 

 Quercus, Sassafras, etc., and what is noticeable is the almost entire 

 absence in this group of any kind of serrate leaves. Prof. Lesquereux 

 also remarks, "There is also in the flora of the Eocene of the Eocky 

 Mountains a marked preponderance of leaves with entire borders. 

 The serrate leaves appear in the Miocene, with Acer, Alnus, Corylus, 

 and become predominant in the Pliocene of California, where TJlnus, 

 Planera, Celtis, Carya abound, though these genera are not more in 

 the flora of the Pacific Slope." ^ 



The Benton, Niobrara, Pierre and Foxhills groups are undoubtedly 

 Cretaceous, but the Fort Union or Lignite group, which is largely 

 developed in the North-west, is somewhat debateable ground, for 

 although usually regarded as Tertiary from its flora, Prof. Cope saj^s 

 of the beds in the Missouri valley : " The presence of the orders 

 Sauropterygia and Dinosauria establishes conclusively the Cretaceous 

 and Mesozoic character of that fauna." ^ 



M. Lesquereux and Dr. Newberry consider this series of beds as of 

 Tertiary age, and some of them to be as high as the Miocene. Prof. 

 Cope regards the evidence derived from the Molluscs in the lower 

 beds, and the Vertebrates in the higher, as equally conclusive that 

 the beds are of Cretaceous age. There is, then, no alternative but 

 to accept the result, that a Tertiary flora was co7itemporaneous with 

 a. Cretaceous fauna, establishing an uninterrupted succession of life 

 across what is generally regarded as one of the greatest breaks in 

 geologic time.^ As bearing on the subject of the Lignitic formation 

 considered as Eocene, Prof. Lesquereux remarks : " The presence of 

 deep marine species in strata overlying remains of more recent ones 

 indicates a local subsidence which should be considered as an ex- 

 ceptional case, unimportant indeed in comparison to the persistence 



of general characters Shall we admit as Cretaceous all 



these land formations bearing from top to bottom evident Eocene 

 characters, on account of some isolated Cretaceous deposits locally 

 spread over them ; or shall we consider the whole presenting general 

 characters positive enough to force its separation into a new group, 

 and call it Eocene ? . . . . We do not, and cannot call the Coal- 



^ Bulletin of the U.S. (reol. and Geogr. Survey of the Territories, No. 2, p. 61. 



^ Ibid. p. 7. In a communication to the Academy of Natural Sciences, Phila- 

 delphia, Jan. 20 and 27, 1874, Prof. E. D. Cope has further corroborated the 

 Cretaceous age of the lignite-beds of North-east Colorado and Fort Union by the 

 discovery of remains of Dinosauria [Hadrosaiirus, Folyonex, etc.), as well as of 

 Tortoises and Crocodiles. ^ Ibid. p. 16. 



