76 INDEX TO THE STEATIGRAPHY OF NOETH AMERICA. 



The main occurrence of the Bhss sandstone is along the eastern slopes of the Franklin 

 Mountains, but the considerable faulting to which the range has been subjected causes its dis- 

 tribution to be very irregular. The Bliss is a massive, fine-textured, brownish sandstone that 

 varies from a few feet to slightly more than 300 feet in thickness. The lower beds are indurated 

 and are practically quartzites and at the base of the formation the strata are coarser textured, 

 locally are conglomeratic and contain pebbles of the underlying rocks. The sandstone is com- 

 posed of small grains of quartz embedded in a matrix of sericite and kaolin. In places the 

 Bliss sandstone is in contact with granite of post-Carboniferous age and elsewhere it rests on 

 rhyolite porphyry, of which it contains rounded pebbles in the basal beds. In the central part 

 of the Franklin Mountains the sandstone thins out and locally disappears, and the overlying 

 Umestone, containing a basal conglomerate, lies directly on the rhyolite porphyry. 



Annelid borings both perpendicular and parallel to the bedding occur abundantly in the 

 Bhss sandstone. Other fossils are rare, but in places in the lower strata some brachiopod 

 shells have been found. Of these Mr. Walcott has identified Lingulepis acuminata, Oholus 

 matinalisCi) , and fragments of Lingulella which determine the Cambrian age of the rocks and 

 indicate that either the upper or middle division of the system is here represented. 



The Van Horn is a medium to coarse-textured cross-bedded sandstone that is banded with 

 thin lenses of conglomerate. The formation is of a prevailing brick-red color in its lower part, 

 which becomes paler toward the top, where the color fades away and the sandstone is white. 

 The conglomerate lenses vary from a few inches to about a foot in thickness and are irregularly 

 distributed throughout the formation. At the base the pebbles are composed of fragments of 

 the underlying rocks and consist of quartz schist, fine-textured red sandstone, cherty hmestone, 

 porphyry, and quartz, while the conglomerate in the upper part of the formation consists chiefly 

 of well-rounded quartz pebbles. The sandstone hkewise varies in composition, its lower part 

 being composed of quartz and decomposed feldspar grains while the upper portion is prevailingly 

 quartzose. The formation varies from a few feet to 700 feet in thickness and averages about 

 400 feet. 



The Van Horn sandstone unconformably overlies highly tilted metamorphosed rocks and 

 is overlain in places by the El Paso limestone (Ordovician) , and elsewhere by the Hueco hme- 

 stone (Carboniferous). The upper part of the formation contains numerous annelid borings and 

 fucoid-like remains, but no characteristic fossils have been found in the sandstone and its age 

 therefore is undetermined. 



The presence of sandstone at the base of the Paleozoic section in southwestern United 

 States has been noted wherever observations have been made, and it is suggested that the Bhss 

 and Van Horn sandstones are the probable equivalent of the Tonto sandstone of the Grand 

 Canyon, the Bolsa quartzite of Bisbee, the Coronado quartzite of Clifton, the Reagan sandstone 

 of Oklahoma, and the Cambrian sandstone of the central Texas Paleozoic area. 



The El Paso Hmestone outcrops in the Franklin and Hueco mountains in the El Paso quad- 

 rangle and in Beach and Baylor mountains in the Van Horn quadrangle. The formation is 

 typically a massive gray magnesian hmestone which contains the same fauna in both regions. 

 In the El Paso area the formation is about 1,000 feet thick, the lower 100 feet of which is char- 

 acteristically arenaceous and weathers brownish. A distinctive feature of the middle portion 

 of the formation is the presence of thin connected nodules of brown chert arranged in irregular 

 steaks parallel to the bedding. This Umestone hes apparently conformably on the Bhss sand- 

 stone, but, as already stated, in the central part of the Franklin Mountains the Bliss sandstone 

 is locally absent and the El Paso limestone rests directly on pre-Cambrian ( ?) rocks with a basal 

 conglomerate varying up to 20 feet thick composed of rounded pebbles of rhyohte porphyry in a 

 calcareous matrix. In the Van Horn quadrangle the El Paso hmestone does not contain the 

 cherty layers that are characteristic of the nxiddle parts of the formation in the Franklin Moun- 

 tains, and 50 feet above the base of the formation a thin bed of white sandstone is present. In 

 this region there are indications of an unconformity at the base of the hmestone marked by a 

 sUght undulatory contact between the El Paso and Van Horn formations. 



