64 H. E. Gregory — A Geologic Reconnaissance 



TV. Section of HuayUabamba formation on south branch 

 of Rio Hnaccoto. 



Strike N 70° W; dip 40° S. 



Feet. 



1. Shale, chocolate to dark red; friable 10 



2. Sandstone, brown, with included fragments of chocolate 



shale 0.2 



3. Shale, chocolate 0.2 



4. Sandstone, brown 6 



5. Shale, chocolate, with lenses of sandstone 7 



6. Sandstone, brown 4 



7. Shale, chocolate, with thin beds of sandstone 12 



8. Sandstone, brown 3 



9. Shale, chocolate 2.6 



10. Sandstone, brown, with two 3-inch bands of chocolate 



shale 77tt 13 



11. Shale, chocolate 4.5 



12. Sandstone, brown 3 



13. Shale, chocolate 1.5 



14. Sandstone, brown; with 5-inch lens of chocolate shale 12 



15. Shale, chocolate 2 



81 



The Hnaccoto section is about 1,000 feet, stratigraphically, 

 below the strata included in Section III. The distinction 

 between sandstone and shale in this section is not well marked. 

 All the shale beds are arenaceous, and the sandstone strata 

 are laminated, rarely cross-bedded. Intermittent exposure to 

 the sun is attested by mud cracks and films of glistening, 

 compact mud which mark the division planes between lamina?. 



In a series of strata at Cerro Picol, whose position in the 

 stratigraphic column is below the beds of Section IV, thin 

 beds of dark-red arenaceous limestone were noted, and the 

 chocolate-colored shales were found to be more calcareous than 

 /at the localities represented by Sections III and IV. Also, 

 thin beds of gray sandstone, banded, minutely cross-bedded, and 

 containing pebbles of gray shale, chocolate-colored shale, and 

 red limestone, constitute about 15 per cent of the 700 feet 

 of the strata examined. 



. At Ccorao Pass, at an elevation of 12,500 feet, thin bands 

 of brown argillaceous limestone are interbedded with the 

 familiar brown sandstones, chocolate-colored shales, and gray 

 sandstones. 



