572 w. T. liEE — Stratigraphy of coal fii^lds of :N[e;w MEixico 



eastern part of the San Juan Basin, known also as the San Juan Eiver 

 region (107)/ from the Colorado-New Mexico line southward to Cabe- 

 zon, and the smaller fields to the southeast, namely, the Eio Puerco, 

 Tijeras, Hagan, and Cerrillos coal fields. Observations were also made 

 near Durango, in southwestern Colorado, in the type area of the Mesa- 

 verde formation. In addition to the observations made in these fields 

 during the summer of 1911, some of the unpublished results previously 

 obtained in the Eaton coal field are used. The location of the area de- 

 scribed is indicated on the accompanying sketch map, figure 1. 



Purpose of In^vestigation 



The purjDose of this investigation was to determine the relation of the 

 coal-bearing rocks east of the Eocky Mountains, in southern Colorado 

 and northern Xew Mexico, to the coal-bearing rocks similarly located 

 west of these mountains. The reason for undertaking it may be briefly 

 stated as follows: Until recently the coal-bearing rocks in the Eaton 

 Mesa region east of the mountains were supposed to constitute a single 

 formation, and this was correlated with the Laramie of the Denver Basin. 

 However, a few years ago it was shown that the so-called Laramie of 

 this region consists of two formations separated by an unconformity rep- 

 resenting a time break of considerable magnitude, and that each forma- 

 tion was characterized by an extensive and well preserved flora. The 

 flora of the lower formation, according to Doctor Knowlton, seems to 

 prove that it is older than recognized Laramie, while that of the upper 

 formation proves that this formation is post-Laramie in age. 



West of the mountains, in the San Juan Basin, two coal-bearing for- 

 mations occur in the upper part of the Cretaceous series. The younger 

 one, at the top of the Cretaceous, has been correlated somewhat doubt- 

 fully with the Laramie, and the older one, or Mesaverde, is of Montana 

 age and is separated from the "Laramie" by a thick formation of marine 

 shale — the Lewis. 



These two large areas of coal-bearing rocks — the Eaton Mesa region 

 and the San Juan Eiver region — are situated on opposite sides of the 

 Eocky Mountains, only 90 miles apart, but, unfortunately, none of the 

 Cretaceous rocks extend continuously around the mountains to connect 

 these two principal areas, so that continuous tracing of formations from 

 one to the other is impossible. However, certain small isolated coal fields 

 at the southern end of the main range of the mountains help to bridge 



2 The references to the publications cited in this paper are Indicated by numerals, 

 which correspond with those in "Bibliography and Notes" on pp. 659-686. 



