18 



LARAMIE FLORA OF THE DENVER BASIN. 



ing that the separation of the Arapahoe and 

 Denver did not constitute redefinition,- and 

 finally, following a suggestion made by himself 

 in 1892, proposed for the latter and their 

 equivalents the term Shoshone group. He 

 said: 



It is proposed to apply the term Shoshone group to the 

 deposits which unconformably succeed the Laramie and 

 to their equivalents and which are overlain by the Fort 

 Union or Wasatch beds when they are present. 



In this paper Cross reviewed briefly the data 

 bearing on the age of these post-Laramie beds 

 and concluded as follows : 



In the preceding discussion I have avoided the question 

 as to the age of Shoshone beds, whether Cretaceous or 

 Eocene. I desire now to urge their reference to the 

 Eocene. The Denver beds were originally referred by 

 me to the Eocene, but the great weight attached to the 

 Mesozoic affinities of the vertebrate fauna by paleontolo- 

 gists led to a tentative acquiescence in the assignment of 

 the Arapahoe and Denver formations to the Cretaceous 

 in the Denver monograph. 



RATON MESA REGION OF COLORADO AND NEW 

 MEXICO. 



In 1907 a series of observations were begun 

 in the Raton Mesa region of southern Colorado 

 and northern New Mexico, which were found 

 ultimately to have an important bearing on the 

 formations under discussion in the Denver 

 Basin. 



The Canon City field of Colorado, although 

 slightly extralimital, is here included in the 

 Raton Mesa region, which really begins with 

 Walsenburg, Colo., and vicinity and extends 

 southward to Cimarron River, N. Mex. The 

 early history of geologic exploration and inter- 

 pretation in this region has already been given 

 in the historical review of the time which pre- 

 ceded the establishment of the term Laramie, 

 and in this connection it is only necessary to 

 mention the names of. Le Conte, Lesquereux, 

 Hayden, Newberry, and Stevenson as among 

 those who took principal parts in the discus- 

 sion. The section of coal-bearing rocks in this 

 region was considered by one set of students 

 as being more or less directly the equivalent of 

 the "Lignite group'' of the north and Tertiary 

 in age. The opposing students regarded the 

 age as Cretaceous, but when the Laramie was 

 established by King the definition appeared to 

 fit the Raton Mesa section, and consequently 

 the beds in this area soon came to be accepted 

 as of Laramie (Cretaceous) age. It should not 



be overlooked, however, that from his studies 

 of the fossil plants Lesquereux was led to 

 insist that the flora of certain localities within 

 this area, notably Raton Pass and Fishers Peak, 

 indicated a correlation with the so-called "Eo- 

 lignitic" ( = Wilcox formation) of the Gulf 

 region and was of Tertiary age. 



A critically annotated historical review of 

 geologic and paleontologic literature on this 

 region is given in a recent paper by Lee and 

 Knowlton, 66 to which the reader is referred 

 for full particulars. In the present connec- 

 tion it is sufficient to begin with the time- 

 about 1900— when geologists had reached a 

 general agreement that the coal-bearing rocks 

 of the Raton Mesa region are of Laramie age 

 and, moreover, that sedimentation had been 

 continuous and uninterrupted throughout the 

 deposition of this section. Thus, , in my 

 "Catalogue of the Cretaceous and Tertiary 

 plants of North America," 67 published in 

 1898, the plants from the Raton region were 

 referred to the Laramie as then currently 

 accepted. In Newberry's long delayed mono- 

 graph on the later extinct floras of North 

 America, 68 also issued in 1898, the few species 

 from this region .were referred without ques- 

 tion to the Laramie. In the Walsenburg and 

 Spanish Peaks geologic folios, by R. C. Hills, 69 

 issued in 1900 and 1901, respectively, the pro- 

 ductive coal measures were referred to the 

 Laramie without qualification. 



In 1909, however, W. T. Lee 70 published a 

 short paper under the title "Unconformity in 

 the so-called Laramie of the Raton coal field, 

 New Mexico," in which the following was 

 given as the thesis: 



The purpose of this paper is to describe an uncon- 

 formity hitherto unknown that is of more than ordinary 

 interest because it divides rocks previously referred to 

 the Laramie into two distinct formations. * * * Dur- 

 ing the time interval represented by the unconformity 

 the sedimentary rocks previously laid down within the 

 Raton field were subjected to erosion for a considerable 

 length of time, and the Rocky Mountains west of this 

 field were elevated and eroded to a depth of several 

 thousand feet. 



Lee further pointed out that 



K Lee, W. T., and Knowlton, F. H., Geology and paleontology of 

 tbe Raton Mesa and other regions in Colorado and New Mexico: U. S. 

 Geol. Survey Prof. Paper 101, pp. 17-37, 1918. 



" Knowlton, F. H., U. S. Geol. Survey Bull. 152, 1898. 



« Newberry, J. S., TJ. S. Geol. Survey Mon. 35, 1898. 



» Hills, R. O, U. S. Geol. Survey Geol. Atlas, Walsenburg folio (No. 

 681, 1900; Spanish Peaks folio (No. 71), 1901. 



™ Lee, W. T., Geol. Soc. America Bui)., vol. 20, pp. 357-358, 1909. 



