G. B. Richardson— Paleozoic Formations. 477 



Annelid borings both perpendicular and parallel to the 

 bedding occur abundantly in the Bliss 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, Obolus matinalis (?) and fragments 

 of Lingtdlela which determine the Cambrian age of the rocks 

 and indicate that either the upper or middle division of the 

 system is here represented. 



Van Horn Sandstone. 



The Van Horn is a medium to coarse-textured cross-hedded 

 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 towards 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 limestone, porphyry and quartz, while the conglomerate 

 in the upper part of the formation consists chiefly of well 

 rounded quartz pebbles. The sandstone likewise varies in com- 

 position ; its lower part being composed of quartz and decom- 

 posed 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 Hneco lime- 

 stone (Carboniferous). The upper part of the formation con- 

 tains 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 Bliss 

 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 sand- 

 stone of Oklahoma and the Cambrian sandstone of the Central 

 Texas Paleozoic area. 



Ordovician. 



El Paso Limestone. 



The El Paso limestone outcrops in the Franklin and Hueco 

 Mountains in the El Paso quadrangle and in Beach and Baylor 

 Mountains in the Yan Horn quadrangle. The formation is 

 Am. Jour. Sci.— Fourth Series, Vol. XXV, No. 150.— June, 1908. 



