422 SIDNEY POWERS— THE SOLITARIO UPLIFT 



clearly a part of the Cordilleran region. The latter is a block-faulted 

 uplift comparable to a horst, which shows very gentle folding. It forms 

 the southern end of the Bend arch. The Paleozoic rocks in the Solitario 

 and Marathon areas show the same northeast-southwest strike, but the 

 continuation of this line of folding has not been traced beneath the 

 younger sediments. On the north side of the Marathon area the Glass 

 Mountains, composed of a great thickness of Permian limestones, mark, 

 locally, the southern limit of a series of Permian sediments unconform- 

 able with the earlier Permian, which extend into New Mexico vv^ith abrupt 

 lithologic change. Somewhere east of the truncated edges of these Per- 

 mian sediments another Bend arch may be found extending toward the 

 Wichita Mountains. Buried granite knobs have been found to extend 

 through Beckham County, Oklahoma ; Amarillo, Texas, and Anton Chico, 

 Xew Mexico, and this evidence may be interpreted as indicating a lack 

 of connection between the Arbuckle and Wichita Mountains and the Bend 

 arch-Marathon-Solitario folding. All this folding is, however, Appa- 

 lachian, as long ago pointed out by R. T. Hill,^ because the Cordilleran 

 folding began with the Laramie revolution.*' Contrasting the Cretaceous 

 Cordilleran and Paleozoic Appalachian structures, the strike of the 

 former is northAvest-southeast, the latter at right angles. Undoubtedly 

 the combination of these lines of folding has been an important, if not a 

 decisive, factor in the formation of domes such as the Solitario and 

 Marathon. The exposures of Pennsylvanian and Permian rocks at 

 Shatter and probably west of the Chinati Mountains are accidental, 

 because they are apparently the tilted edges of east-west fault blocks 

 exposed in the deep dissection of the volcanics by Cibolo Creek. Similar 

 exposures in Mexico are reported to the writer by Dr. Udden. 



Detailed Geology 



stratigraphy 



Fossils in pre-Cretaceous rocks are difficult to find, and the age deter- 

 minations are made by analogy with the Marathon region, where excellent 



^ Physical geography of the Texas region. U. S. Geol. Survey, topographic atlas of 

 the United States, Folio 3, 1900, p. 4. 



^ Willis T. Lee disagrees with this reasoning in his paper on "Granite in eastern New 

 Mexico wells" (Bull. Amer. Assn. Pet. Geol., vol. 5, no, 2, 1921, p. 165), where he states: 



"The Pennsylvanian sedimentation was brought to a close in New Mexico by the eleva- 

 tion of mountains which the writer has termed the Ancestral Rocky Mountains. The 

 Pennsylvanian strata were upturned in these mountains, eroded, and probably in some 

 places entirely removed. ... It seems appropriate to regard [the post-Pennsylvanian 

 unconformity] as a major unconformity." 



