608 W. T. LEE STRATIGRAPHY OF COAL FIELDS OF NEW MEXICO 



Durango and nearly as thick in the southern rim of the basin (110, page 

 338), but is thinner in the eastern rim, probably due to the post-Creta- 

 ceous erosion. At Dulce it is only 225 feet thick. This formation lies 

 conformably on Lewis shale, and probably for this reason more than for 

 any other has been called Laramie, although Doctor Cross (75, page 4) 

 several years ago called attention to the fact that investigation had 

 ^^f ailed 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." 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 Cliffs sandstone — contains marine inverte- 

 brates, and the lower part of the coal-bearing rocks above this sandstone 

 contains brackish-water invertebrates, several of which occur in the Mesa- 

 verde of other fields. But higher in the formation the rocks contain 

 fresh-water invertebrates which Doctor Stanton regards as Laramie and 

 fossil plants which Doctor Knowlton regards as older than Laramie. 

 The fossil plants have been included in the table previously given (page 

 606), and from this table, as well as from the accompanying statement by 

 Doctor Knowlton, 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 Avriter is intentionally avoid- 

 ing the introduction 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 desig- 

 nated in some other way depends largely on the final use of that some- 

 what migratory name. But in view of the fact 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 inverte- 

 brates from the upper part are of fresh-water origin and admittedly 

 unreliable for purposes of correlation, and that the plants are of Montana 

 types, serious doubt is cast on tlie Laramie age of the formation. 



TERTIARY AND LATER FORMATIONS 



It is not the purpose of the writer to enter into a discussion of the 

 Tertiary and later formations of IN'ew Mexico farther than is necessary 

 to show that in all of the coal fields described rocks of probable Tertiary 

 age lie unconformably on "Laramie" or older rocks. In the Durango 



