The areas in which the observations forming the basis of this paper were made lie in central and northern New Mexico, around the southern end of the main mass of the Rocky Mountains. The region includes the eastern part of the San Juan Basin, known also as the San Juan River region (107),2 from the Colorado-New Mexico line southward to Cabezon, and the smaller fields to the southeast, namely, the Rio Puereo, Tijeras, Hagan, and Cerrillos coal fields. Observations were also made near Durango, in southwestern Colorado, in the type area of the Mesaverde formation. In addition to the observations made in these fields during the summer of 1911, some of the unpublished results previously obtained in the Baton coal field are used. The location of the area described is indicated on the accompanying sketch map, figure 1.
The purpose of this investigation . . .