560 HEALD AND MATHER RECONNAISSANCE OF EASTERN ANDES 



The light gray beds are gypsiferous and contain many limestone con- 

 cretions. A series of ferruginous shales, gray, brown, and reddish in 

 color, is doubtfully placed in the upper portion of this formation. Both 

 shales and thin sandstones are very micaceous. The mica ranges from 

 microscopic specks to flakes an eighth of an inch in their greatest 

 dimension. 



The sandstones through most of the formation are so thin as to be 

 almost unnoticeable, single beds averaging only a few inches in thickness 

 and aggregate thicknesses of contiguous sandstone beds being commonly 

 less than four feet. Many of these thin sandstones are richly fossil- 

 iferous. 



The upper part of the formation is much more sandy than is the base. 

 This is shown both by an increase in the sand content of the shales and 

 by the presence of massive beds of sandstone. These massive sandstones 

 are gray to tan in color, close textured, line grained, and moderately 

 hard. Individual beds may be as thick as 50 feet, although the average 

 is much closer to 10 feet. 



The Totora is lithologically quite similar to the Pennsylvanian strata 

 of southeastern Oklahoma and, probably like these Pennsylvanian strata, 

 originated by practically continuous sedimentation in a shallow sea, the 

 floor of which sank steadily under the accumulating load of sand and 

 mud. 



MATERAL FORMATION 



The Materal formation, named from the village of Materal, on the 

 Santa Cruz 'Frail, is believed to rest unconformably on the Totora, 

 although this unconformabilitv was not actually observed. However, 

 the striking difference in lithology of the two formations signifies very 

 different conditions of sedimentation or sources of materials and sup- 

 ports a belief in a time break between the two formations. 



The age of the Materal was not determined, but it is ascribed to the 

 Carboniferous because of its relation to the underlying Totora beds and 

 to the overlying Bermejo formation, which is thought to be Permian. 

 However, it must be recognized that the age of the Bermejo is also in 

 doubt. 



The thickness of the formation could not be closely estimated, for 

 folding and faulting had complicated the section where the traverse 

 crossed it. However, it may be confidently stated that this thickness 

 exceeds 2,000 feet and very probably 4,000 feet. 



The most prominent beds in the formation are heavy sandstones, 

 although shales may predominate in aggregate thickness. No lime- 



