DESCRIPTIVE DETAILS : CERRILLOS FIELD 657 



The rock formations near the base of the Cretaceous are well exposed 

 in Canyon del Yeso, about 2 miles north of Galisteo Creek, where the 

 following section of them was measured. Fossils were collected from 

 these formations and included in the descriptive section. That part of 

 the Mancos shale lying stratigraphically above this section was found to 

 be fossiliferous in many places, but it does not lend itself readily to 

 measurement. 



Section of Rocks measured in Canyon del Yeso about 2 Miles North of Gali.steo 

 ' Creek 



Feet 

 Limestone and shale in alternating layers, containing Inoceramus 



lahiatus Schloth. (horizon of Greenhorn limestone) ir» 



Shale, containing Prionotropis sp 1(»()± 



Sandstone (Tres Hennanos), hard, quartzose, with sparkling sand 

 grains, brown to yellow, in thin irregular layers with numerous worm 

 borings and varlons indefinite markings. In the lower 10 feet the 



layers of sandstone are separated by thin layers of shale 25 



Sandstone, containing Inoceramus sp. and Pinna sp 10 



Shale (Gastropod zone), dark-colored, with concretions of earthy lime- 

 stone 20 feet from the top. Some of the concretions are fossiliferous 

 and weather to a rustj' yellow powder around the fossils, rendering 

 specific idenfification difficult. From these concretions were obtained 

 Ostrea sp. ; Exogyra columhella Meek; Plicatula sp. ; Lima sp. ; Pinna 



sp. ; AncJiura^ sp. (U. S. G. S. locality No. 3536) 70 



Sandstone (Dakota), conglomeratic at the base 40 



Shale, sandy, near the top 10 



Sandstone, coarse-grained, cross-bedded, white 70 



Sandstone and shale, variegated ( Morrison ) 



An effort was made to recognize in this section the several zones de- 

 scribed from the lower part of the Eogers section located 3 miles farther 

 south. The sandstone and shale, here referred to the Morrison, is similar 

 lithologically to the variegated beds belo\v the 10-foot conglomerate in 

 the Morrison of the Rogers section. The -lO-foot conglomerate sandstone 

 is referred to the Dakota and the lower sandstone, 70 feet thick, is prob- 

 ably also Dakota, although it may be equivalent to the beds of the Rogers 

 section lying below the conglomeratic Dakota and there referred with 

 some doubt to the Morrison because it differed lithologically from the 

 overlying Dakota. The rocks above the Dakota in Canyon del Yeso are 

 the same as those similarly situated in the Rogers section. The 70-foot 

 shale corresponds in position to the shale containing the Gastropod zone 

 and the 35 feet of sandstone above it to the Tres Hermanos sandstone of 

 the Rio Puerco field. The Greenhorn limestone horizon was recognized 

 by its characteristic fossil, Inoceramus lahiatus. Two hundred feet or 



