68 



II. E. Gregory- — A Geologic Reconnaissance 



VI. Section of Huayallabamba formation, including the 

 Molle-Orcco conglomerate member, on west bank of Rio 

 Huancaro below the mouth of Rio Chchocco. 



Northeast limb of syncline. Strike N 80° ± W; dip 90°-10° S. 



1. Sandstone, gray on surface, gray-brown below, and 

 conglomerate, cross-bedded, in places banded with 

 black sand. Conglomerate constitutes about 30 per 

 cent of bed and is arranged in lenses 10 to 100 feet 

 long, 1 inch to 4 feet wide, in irregular masses 3 to 

 6 feet in diameter, and as isolated strings of pebbles ; 



Feet. 



Fig. 35. 



Fig. 35. General view of strata comprising the Huayllabamba forma- 

 tion, including beds of the Molle-Orcco conglomerate member. Ayusbamba 

 trail. 



pebbles reach a maximum size of 8 inches and average 

 about 1 inch; types noted include quartz of various 

 colors, feldspar, biotite granite, porphyritic trachyte, 

 diabase, green, yellow, and brown quartzite; horn- 

 stone, slate, brown sandstone, brown shale, and lime- 

 stone. The pebbles are fairly well worn and rounded 

 and are embedded in sand held together by ferric, 

 argillaceous, and calcareous cement 30 



2. Sandstone, dark red, friable, calcareous 3 



3. Sandstone and conglomerate like ]STo. 1, except for 



abundant flat pebbles of dark-red sandstone and shale 8 



