STRATIGRAPHY 561 



stones were seen. The sandstones are for the most part massive, fine 

 textured beds, ranging in color from gray to red, with intermediate 

 shades of yellow, tan, and brown. Some of them are conglomeratic, so 

 there mnst also be some coarse sandstones, although none were specifically 

 noted. One sandstone bed with a thickness of about 600 feet was seen, 

 but the average thickness is probably 40 feet or less. Both sands and 

 conglomerates are formed clominantly of white or colorless quartz. The 

 conglomerates also contain some flesh-colored feldspar. 



The shales are light colored, ranging through a variety of shades of 

 gray, green, and red. No black shales like those of the Totora formation 

 are present, unless, indeed, an exposure about 10 miles east of Materal, 

 which was believed to represent Totora shale, unconformably below the 

 Materal, should really be ascribed to the latter. All the shales seen 

 appeared quite massive, with little fissility or lamination. 



The outcrop of this formation is crossed by the Santa Cruz Trail 

 between San Ysidro and Samaipata. A point midway on the exposure 

 would be about 70 miles west and 25 miles south of Santa Cruz. 



The Materal beds are thought to be continental in origin. The con- 

 glomerates are almost certainly fluviatile, and the red and green shales 

 are probably in large part lake deposits. The perfect sizing and round- 

 ing of the grains in one sandstone bed suggested windwork, but support- 

 ing evidence, such as cross-bedding and ripple-marks, was lacking. The 

 feldspar in the conglomerate suggests a different source for the materials 

 that formed the Materal and those that make up the Totora, and relates, 

 the Materal more closely to the overlying Bermejo formation, in which 

 feldspar and fragments of granitic rock are locally abundant. 



BERMEJO FORMATION 



Unconformably above the Materal formation is a thick series of heavy 

 sandstones, massive shales, and thin beds of tillite aggregating in thick- 

 ness about 10,000 feet, which the writers have called the Bermejo forma- 

 tion after the settlement of Bermejo, near which it is developed. 



The age of the Bermejo was not discovered. It is thought to be 

 Permian, but the evidence for this assignation is inferential. The 

 unconformity that separates it from the underlying formations is pro- 

 found, probably representing in places the entire thickness of the Materal 

 formation and much of the Totora. The Bermejo is, therefore, unques- 

 tionably post-Devonian and probably post-Pennsylvanian. In the region 

 to the south it lies below the Calcareo-dolomitico of Steinman, which he 

 assigned to the Cretaceous on the basis of fossils. Its tillite beds sug- 

 gest contemporaneity with similar deposits in Brazil, which Branner 



