HISTORICAL REVIEW OF THE LARAMIE PROBLEM. 



19 



The upper formation has the stratigraphic position of 

 the Arapahoe of the Denver Basin but contains a flora 

 apparently more closely related to that of the Denver 

 formation than it is to the Laramie of the Denver Basin. 

 The lower one has the stratigraphic position of the Lara- 

 mie of the Denver Basin but contains a flora that is ap- 

 parently older than Laramie. 



As regards the significance of this uncon- 

 formity Lee added: 



There are several possibilities of interpretation, as will 

 be pointed out in the following pages, but the one con- 

 sidered most probable is that the uplift and erosion rep- 

 resented by the unconformity were contemporaneous 

 with the post-Laramie uplift and erosion described by 

 Cross and others from the Denver region. 



Without xmduly anticipating, it may be 

 stated that subsequent work has entirely 

 confirmed this interpretation. 



In 1910 G. B. Richardson, 71 in a short report 

 on the coal resources of the Trinidad coal field 

 of Colorado, noted the conglomerate described 

 by Lee in the report on the Raton coal field as 

 marking the unconformity and said: 



The significance of the conglomerate in the Trinidad 

 field remains to be determined. • Occurring intermittently 

 in the midst of coal-bearing rocks, it may represent only a 

 local change in conditions of deposition, or, as maintained 

 by Lee for a conglomerate in the Raton field, presumably 

 the same as trie one just described, it may mark an uncon- 

 formity contemporaneous with the post-Laramie uncon- 

 formity of the Denver Basin. * * * The final word 

 concerning the age of the rocks above and below this con- 

 glomerate in the coal measures, involving its significance 

 as a hiatus marker, must come from the paleontologist. 



As the paleobotanic data then tentatively 

 supplied by me were more or less conflicting 

 and inconclusive, Richardson wisely enough 

 concluded that 



Until further paleobotanical knowledge is available,- the 

 age of these rocks must remain unsettled. For the present 

 it seems best to retain the old nomenclature and to refer 

 the strata occurring between the Trinidad sandstone and 

 the'Poison Canyon formation to the Laramie. 



In the same volume with Richardson's report 

 is a paper by C. W. Washburne " on the Canon 

 City coal field, Colo., in which he stated that 



The Laramie formation, which contains all the coal beds 

 of the Canon City field, rests conformably on the Trinidad 

 sandstone and is unconformably overlain by the Arapahoe 

 (?) conglomerate. The productive division of the forma- 

 tion is the lower 600 or 700 feet. 



Although Washburne admitted that the 

 "upper part of the coal measures contains a 



" Richardson, G. B., The Trinidad coal field, Colo.: U. S. Geol 

 Survey Bull. 381, pp. 379-446, 1910. 

 « U. S. Geol. Survey Bull. 381. pp. 341-378, 1910. 



flora equivalent to that of the Laramie for- 

 mation of the Denver Basin, while the lower 

 part contains a flora of upper Montana age," 

 he concluded that " there seems no good reason 

 for separating these lower beds from the Lara- 

 mie, even though they contain an upper 

 Montana flora." 



The work on the stratigraphy and paleo- 

 botany of this region was continued by Lee 

 and Knowlton, 73 and their results were presented 

 for publication early in 1913. These results 

 I briefly summed up in May of that j T ear as 

 follows: 74 



In 1907 W. T. Lee began the study of the coal in the 

 Raton field, and while prosecuting this work he discovered 

 the presence of an unconformity in the midst of the section 

 of coal-bearing, supposed Laramie rocks. This uncon- 

 formity was traced throughout the entire Raton Mesa and 

 subsequently was carried around the southern end of the 

 mountains and well up along their western front. The 

 rocks below the unconformity, to which the name Vermejo 

 formation has been given, have a maximum thickness of 

 only about 375 feet, while the rocks above the uncon- 

 formity, now called the Raton formation, are about 1,600 

 feet in thickness. In some places the Raton formation 

 rests on the full thickness of the Vermejo formation, while 

 in other localities the Vermejo is greatly reduced, and in 

 at least one place the entire Vermejo, together with the 

 underlying Trinidad sandstone, has been removed and the 

 Raton rests directly on Pierre. 



When the unconformity had been demonstrated, it 

 became of the greatest interest and importance that the 

 fossil plants should be studied to ascertain their bearing, 

 first, on the distinctness of these two formations, and, 

 second, on the question of age. * * * The total flora 

 of the Raton Mesa region comprises 257 forms, of which 

 number 106 belong to the lower, or Vermejo and Trinidad 

 formations, and 151 to the upper, or Raton formations. 

 Only 4 species have been found. to cross the line of the 

 unconformity, which is taken as pretty conclusive evi- 

 dence of the distinctness of the two formations. * * * 

 The Vermejo formation is shown by the plants to be Creta- 

 ceous (Montana) in age, being in the approximate position 

 of the Mesaverde. 



The Raton formation is shown to be essentially of the 

 same geologic age as the Denver formation of the Denver 

 Basin and of the Wilcox formation of the Gulf region, the 

 latter being indisputably of Eocene age. The conclusion 

 is therefore reached that the Raton and Denver formations 

 are Eocene in age. 



In the meantime, as indicated above, Lee had 

 continued the studies from Raton Mesa around 

 the south end of the Rocky Mountains and well 



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

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

 Survey Prof. Paper 101, 1918. 



« Knowlton, F. H., Results of a paleobotanical study of the coal- 

 bearing rocks of the Raton Mesa region of Colorado and New Mexico; 

 Am. Jour. Sci., 4th ser., vol. 35, pp. 526-530, 1913. 



