720 



JAMES H. GARDNER 



of this basin is more marked since the latter consists largely of massive 

 brown sandstones alternating with drab, clay, and arenaceous shale 

 together with local carbonaceous shale and coal beds. 



The structure in the area under discussion, with the exception of 

 unconformable relationships in strata, is such as is common around 

 the margins of most of the minor basins in the Rocky Mountain 

 province. Steeply inclined strata limit the older sedimentary rocks 

 along the boundary of the Nacimiento Mountains, the dips decreas- 

 ing westward toward the interior of the San Juan Basin. (See 



Fig. 5. — Upper escarpment of Nacimiento group, four miles southwest of Naci- 

 miento, New Mexico. 



sketch map, Fig. i.) Near the mountains, this inclination varies from 

 35° north of Gallina to more than 90° at Copper City and northward. 

 In the latter district, the fold is overturned and dips 70° eastward 

 toward the mountains. All the sedimentary formations above the 

 Jurassic have this inclination with the exception of the Wasatch. 

 About ten miles northwest of Gallina the Wasatch has an inclination 

 of about 10° west of south as mentioned by Cope^ and verified by the 

 writer. The dip in that vicinity is apparently local and is of more 

 recent date than any uplift in the Nacimiento Mountains as shown 

 by the fact that the Wasatch beds rest nearly horizontally against the 

 crystalline rocks of those mountains between Gallina and Nacimiento. 



