DESCRIPTIVE DETAILS : CERRILLOS FIELD 



647 



probable that the 1,602-foot hole extends entirely through the Mesaverde 

 formation. The surface in the center is occupied by the Galisteo sand- 

 stone and younger rocks, but the underlying Mesaverde reappears from 

 beneath them with opposite dip at the eastern extremity of the basin and 

 was observed near the town of Galisteo, although no details of it were 

 obtained there. However, at the southeastern extremity of the basin one 

 of the Mesaverde coals has been developed at Omera mine. A section of 

 the rocks exposed near this mine was measured. The dip is low, and the 

 thicknesses given in the following section were obtained by pacing across 

 the outcrop and correcting for dip. Hence the section is approximately 

 correct, but it is presented only for the purpose of showing the relation 

 of the Mesaverde formation to the underlying Mancos shale and to the 

 overlying Galisteo sandstone. 



Section of Rocks measured at Omera Mine, ahout 18 Miles Southeast of 



Cerrillos, New Mexico 



Feet Inches 



Conglomerates base of Galisteo sandstone. 



(Unconformity.) 



Coal (Omera mine) 2± 



Shale, carbonaceous G 



Shale, with layers of sandstone and cone-in-eone 

 sti*ucture limestone (not continuously exposed) . . 75 



Sandstone 100± . . 



Mesaverde i Shale, Carbonaceous in some places, with lenses 

 and concretions of sandstone, and cone-in-cone 

 sti*ucture limestone. Fossil plants at the base. . . 85 



Coal 4 



Shale 5 



Sandstone, massive, yellow; contains fossil shells.. 200± .. 



Shale (Mancos) with a sandy transitional zone at 

 the top. Concretions of fossiliferous limestone 

 occur 100 to 150 feet from the top ; containing 

 Exogyra ponderosa Roemer ? ; Anomia sp. ; Ino- 

 ceramus sagensis Owenj ? ; Inoceramus sp. ; Cucul- 

 Icea sp. ; Gyprimeria sp. ; Volutoderma 1 sp. ; 

 Nautilus sp. ; Baculites sp. ; Mortoniceras sp. re- 

 lated to M. delawarense (Morton) ; Placenticeras 

 sancarlosense Hyatt; Placenticeras sp. — very 

 large specimens, apparently distinct from either 

 of the foregoing (U. S. G. S. locality No. 7180). 

 A few hundred feet lower in this shale the follow- 

 ing fossils occur: Crassatellites shumardi Meek ?; 

 Mactra sp. ; Gyrodes sp. ; Volutodermal sp. ; 

 Actceon ? sp. (U. S. G. §. locality No. 7181) 



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