74 RIO GRANDE COAL FIELDS OF TEXAS. [bull. 164. 
prises the following mountains: The Chinati, Vieja, Van Horn, Car- 
rito, Diablo, Prieta, and Cornuda. Eagle Mountain lies a short 
distance west of the axis of the chain, opposite Bass Canyon. The 
Sierra Blanca are isolated peaks northwest of Eagle Mountain. West 
of Sierra Blanca is the Quitman system, with a NW.-SE. trend. 
Beginning at its southeast end and going northwest, it is composed of 
the Quitman, Malone, Finlay, and Hueco mountains. Still farther 
west are the Organ Mountains, whose axis extends from north to 
south. East of the Vieja Mountains are the higher ranges, known as 
the Guadalupe, Davis, and Chisos groups, which constitute the eastern 
front of the whole Trans-Pecos mountain region. 
The exact localities studied were: (1), The isolated peak, belonging 
to the Vieja Mountains, 6 miles west of south from Chispa; (2) the 
vicinity of San Carlos; (3) the western side of the railroad from 
Chispa summit (the pass between the Van Horn and Vieja mountains) 
to a point 13 miles from Chispa, going southward toward San Carlos. 
LITERATURE. 
Very little has been written concerning this area. W. H. von Stree- 
ruwitz has published a few remarks in the reports of the Geological 
Survey of Texas. In the fourth annual report of that survey, A. 
Osann makes some interesting notes on the igneous rocks. On pages 
386 and 387, Vol. VI of the bulletins of the the Geological Society of 
America, E. T. Durable gives a general section of the Vieja Mountains 
at San Carlos. 
TOPOGRAPHY AND STRUCTURE. 
For the details of the topography the Chispa and San Carlos topo- 
graphic sheets of the United States Geological Survey must be consulted. 
Many geologists have noted in Trans-Pecos Texas the peculiar 
desert valleys or basins, filled with detritus, lying between the moun- 
tains of the region, and the abrupt manner in which the mountains 
rise from them. (PL VI.) Chispa, at an altitude of 4,082 feet, is 
situated in such a basin valley, which is bounded on the south and west 
by the Vieja and Van Horn mountains, respectively, and on the north 
and east by outlying westward members of the Davis ranges. 
About 6 miles southwest of Chispa there is a saddle or pass, known 
as Chispa Summit, which separates the Vieja Mountains on the south- 
east from the Van Horn Mountains on the northwest. The altitude 
of this saddle is a little less than 4,250 feet. On its southern slope 
Van Horn Creek rises. This creek flows through a valley, some 5 or 
6 miles wide, in a general southerty direction, into the Rio Grande. Its 
elevation where it passes from the Chispa quadrangle is less than 3,300 
feet. On its east side, and subparallel to it, are the Vieja Mountains, 
the altitude of whose crest varies from 5,250 to a little over 6,000 feet 
