60 



LARAMIE FLORA OF THE DENVER BASIN. 



the Rocky Mountains, from their west of 

 south course through Colorado, turn north- 

 westward through Wyoming toward the Yel- 

 lowstone National Park. With this area is 

 also considered a long, narrow area extending 

 southward from the vicinity of Rawlins, Wyo., 

 into Routt County, Colo., and connecting 

 through the Elkhead Mountains with the 

 Yampa coal field, which is separated only by 

 the Axial Basin from the coal-bearing rocks 

 that more or less completely surround the 

 Uinta Basin. 



East-central Carbon County has been the 

 scene of more or less critical geologic study 

 for nearly 50 years. The historical account of 

 this work is presented in detail on pages 

 61-65 and need not be repeated here, ex- 

 cept in so far as is necessary to keep the 

 problem well in mind. The following is the 

 section of the rocks of the region as worked 

 out by Veatch:' 8 



Feat. 



North Park Tertiary 4, 500 



Unconformity. 



Fort Union ■ 800-2, 000 



' ' Upper Laramie ' ' . 

 Unconformity. 

 "Lower Laramie " . 

 Montana: 



...... i p Qx jjjjj g f t jj e ear i y surveys . \ 



Mesaverde.J ' J [ 



6,000 



6,500 



3,000 

 3,200 

 3,500 



' ' Pierre shale " 

 Colorado: 



Niobrara 800 



Benton 1, 500 



Dakota 150 



Morrison 200 



Marine Jurassic 75 



Red beds '. 1, 650 



Carboniferous ; 1, 800 



Pre-Cambrian crystallines. 



The section of coal-bearing rocks, given a 

 thickness of 12,500 feet by Veatch, was sup- 

 posed, prior to his work in 1906, to be a unit 

 and all referable to the Laramie. Veatch's 

 discovery, of a profound •unconformity, then 

 thought to be similar in position and magni- 

 tude to that detected by Cross in the Denver 

 Basin, naturally made a readjustment neces- 

 sary, and consequently the beds above the 

 unconformity were called the "Upper Lara- 

 mie" and those below it the "Lower Lara- 

 mie." The latter therefore corresponds in 



i» Veatch, A. C, On the origin and definition of the geologic term 

 "Laramie": Jour. Geology, vol. 15, p. 527, 1907. 



position to the Laramie of the Denver Basin, 

 and the present comparison is instituted to 

 ascertain the bearing of the floras on this 

 correlation. 



Fossil plants occur in greater or less abun- 

 dance in connection with the coal, especially in 

 the vicinity of Carbon, where some of the 

 earliest mines were situated, but it now appears 

 that the work of the Hayden and King surveys 

 was all along or south of the Union Pacific 

 Railroad, where the lower division is usually 

 absent, hence the plants studied by Lesquereux 

 were from the "Upper Laramie," and it is now 

 plain why the ' ' Laramie ' ' of this region appeared 

 to be so distinctively Tertiary in facies. Since 

 the importance of having collections from the 

 "Lower Laramie" has become realized plants 

 have been procured from many localities, as is 

 shown by the lists on page 100, where fur- 

 ther data on the geologic occurrence are given. 



It Was evident that much more field work 

 would be necessary in this region before several 

 more or less discordant views could be har- 

 monized. This was finally accomplished by 

 Bowen, and bis results were published in 1918 

 in a paper entitled "Stratigraphy of the Hanna 

 Basin, Wyo." 19 In this paper Bowen made a 

 number of important changes in the interpre- 

 tation of the Carbon County section as given 

 by Veatch. The two sections are given below: 



Section in Carbon County, Wyo. 



Tertiary. 



North Park forma- 

 0-400 feet. 



-Unconformity 



Tertiary (?). 



Cretaceous. 



Bowen, 1918. 



Veatch, 1912. 



Hanna formation, 

 7,000 ± feet. 



-Unconformity- 



North Park Tertiary, 

 4,500 feet. 



-Unconformity 



Port Union forma- 

 tion, 800-2,000 

 feet. 



Ferris formation, 

 6,500 ± feet. 



"Upper Laramie," 

 6,000 feet. 



-Unconformity 



Medicine Bow for- 

 mation, 6,200 ± 

 feet. 



Lewis shale. 



'Lower Laramie," 

 6,500 feet. 



Lewis shale. 



i» Bowen, C F., U. S. Geol. Survey Prof. Paper 108, pp. 227-235, 1918. 



