70 



LARAMIE FLORA OF THE DENVER BASIN. 



that this division is still apparently below the true Fox 

 Hills. This formation is called the Lewis shale. 



Continuing, Cross said : 



Still above the Lewis shale is a second, series of "sand- 

 stones, shales, and coals, bearing some resemblance to the 

 Mesaverde formation but differing in detail. The lowest 

 member of this complex is the "Pictured Cliff sandstone" 

 of Holmes's San Juan section, which he placed in the 

 Fox Hills upon the evidence of invertebrate remains. 

 The remainder was referred to the Laramie, but without 

 fossil evidence. The present survey has also failed to 

 bring to light valid ground for assigning any of the beds 

 in question to the Laramie, while there is some reason 

 to believe that more than the lower sandstone belongs to 

 the Montana group. 



In 1905 F. C. Schrader 4S made a preliminary 

 or reconnaissance examination of the Durango- 

 Gallup coal field, in which he adopted the 

 stratigraphic classification established by Cross, 

 the uppermost coal-bearing sandstone being 

 classed as Laramie?, though no fossil evidence 

 was presented. 



In 1906 more detailed examinations were 

 made in the region by Joseph A. Taff and 

 M. K. Shaler. Taff 49 considered the Durango 

 coal district, which lies just off the southern 

 foothills of the San Juan and La Plata moun- 

 tains. In this report the upper coal-bearing 

 rocks here under consideration were referred 

 without question to the Laramie, though no 

 details were given as to the reasons for this 

 reference. Shaler 's report 50 deals with that 

 part of the Durango-Gallup field lying west of 

 longitude 107° 30'. The beds here in question 

 were also referred to the Laramie without 

 qualification, on the basis, as he stated, of 

 fossils studied by T. W. Stanton and me, 

 though the evidence was not presented in 

 detail. Examination of the original reports 

 on the plants collected by Shaler and others in 

 this region shows that the collections were few 

 and fragmentary and the tendency was to 

 regard them as_ older than Laramie. 



The status of the "Laramie" in the region 

 under consideration is so succinctly summed 

 up by W. T. Lee 51 in his paper on the "Stra- 

 tigraphy of the coal fields of northern New 

 Mexico" that his remarks are quoted entire as 

 follows : 



<3 The Durango-Gallup coal field of Colorado and New Mexico: U. S 

 Geol. Survey Bull. 285, pp. 241-258, 1906. 



* The Durango coal district, Colo.: TJ. S. Geol. Survey Bull. 316, pp." 

 321-337, 1907. 



so A reconnaissance survey of the western part of the Durango-Gallup 

 coal field of Colorado: Idem, pp. 376-426. 



« Geol. Soc. America Bull., vol. 23, pp. 607-608, 1912. 



The "Laramie" formation occurs within the area de- 

 scribed in this paper only in the San Juan Basin. It is 

 more than 1,000 feet thick in the southern rim of the 

 basin but is thinner in the eastern rim, probably due to 

 post-Cretaceous erosion. At Dulce it is only 225 feet 

 thick. The formation lies conformably on Lewis shale 

 and probably for this reason more than for any other has 

 been called Laramie, although Dr. Cross several years 

 ago called attention to the fact that investigation had 

 "failed to bring to light valid ground for assigning any 

 of the beds in question to the Laramie, while there is 

 some reason to believe that more than the lower sand- 

 stone belongs to the Montana group." Since that time 

 a considerable number of fossils, both of invertebrates and 

 of plants, have been collected from these beds in the 

 Durango region. The base of the formation — the Pictured 

 Cliff Bandstone — contains marine invertebrates, and the 

 lower part of the coal-bearing rocks above this sandstone 

 contains brackish-water invertebrates, several of which 

 occur in the Mesaverde of other fields. But higher in 

 the formation the rocks contain fresh-water invertebrates 

 which Dr. Stanton regards as Laramie and fossil plants 

 which Dr. Knowlton regards as older than Laramie. The 

 fossil plants have been given in the table previously 

 given, and from this table, as well as from the accompany 

 ing statement by Dr. Knowlton, 62 it will be seen that the 

 flora differs but little from that of the Mesaverde farther 

 to the south. ^ 



The name "Laramie " is here used for this formation not 

 because the writer wishes to argue for the Laramie age of 

 the rocks, but because the name is in use and because in 

 this paper the writer is intentionally avoiding the intro- 

 duction of new names for rock formations. . It must be 

 noted, however, that while the formation is called 

 "Laramie" it contains a flora which denotes Montana 

 age, having nothing in common with the Laramie flora 

 of the Denver Basin. 



Whether the formation will eventually be called 

 "Laramie" or be designated in some other way depends 

 largely on the final use of that somewhat migratory name. 

 But in view of the facts that many of the species of marine 

 and brackish-water invertebrates from the lower part of • 

 the formation occur in the Mesaverde of other localities, 

 that the invertebrates from the upper part are of fresh- 



9 The statement here alluded to is as follows: "Near Dulco, N. Mex., 

 and near Durango, Colo., there have been obtained two collections of 

 plants from above the Lewis shale in coal-beanng rocks that have been 

 referred to the so-called ' Laramie' of this region. These collections are 

 very full and embrace a number of easily recognized species, hence their 

 identification is satisfactory and complete. These collections prove 

 clearly that these beds do not belong to the Laramie, since, so far as 

 known to the writer, not a single species there present has been found 

 in beds of this age. On the other hand, the plants indicate beyond 

 question that they belong to the Montana, there being, for instance, 

 Fkus speciomsima, Ficus sp. (narrow, 3-nerved type), Fkus sp., type 

 of F. lunccolata, a palm, etc., which link them with the.Mesaverde floras 

 to the south and the beds already discussed in the Raton Mesa region. 

 Associated with these, however, and tending to give them a slightly 

 higher position, though still within the Montana, are such forms as 

 Brachyphyllum, CunniTighamites, GeinUzia, Sequoia, etc., all of which are 

 beyond doubt Montana types not found in the Laramie. 



A number of collections were made by J. H. Gardner in the Ignacio ^ 

 quadrangle, east of Durango, Colo., from beds regarded as the Laramie 

 of that area. The plants in these collections, almost species by species, 

 are identical with the forms from Dulce and near Durango, and I have 

 no hesitation in saying that they occupy the same stratigraphic posi- 

 tion and are the same in age, viz, Montana." 



