DESCRIPTIVE details: CERRILLOS FIELD 655 



The top of the Mancos shale of this section is particularly rich in fos- 

 sils. In the upper 200 feet of the shale were found the species named in 

 the section measured near Eogers mine (numbers 7164 and 7165). An- 

 other collection reported beyond was made at approximately the same 

 horizon north of Galisteo Creek. In commenting on these fossils Doctor 

 Stanton says: "The horizon is believed to be a short distance above the 

 Austin chalk and the Niobrara limestone — that is, in the lower part of 

 the Montana group.'' 



The base of the Mesaverde formation in the Cerrillos field consists of 

 a massive cliff-making sandstone overlain by other sandstones which are 

 softer and somewhat shaly in places. These sandstones form the surface 

 of a dip slope that is unevenly eroded and their measured thickness is 

 open to question. The measurement of 300 feet, shown in the accom- 

 panying section, was obtained by measuring with tapeline across the 

 strike of rocks dipping only 5 to 8 degrees and computing the thickness, 

 from the dip and horizontal distance measured. It is not certain that 

 the dip is constant nor that no faults occur. No coal was found in this 

 lower 300 feet of the Mesaverde, but at neighboring localities thin beds 

 of coal occur in rocks that probably are equivalent to these lowest rocks 

 of the formation. The sandstone contains large yellow concretions, con- 

 sisting of calcareous sandstone, in which marine fossils were found. 

 Some shale occurs, but it seems to be very subordinate in amount. Ap- 

 parently this 300± feet of sandstone corresponds to the part of the 1,602- 

 foot drill record between the lowest shale and the top of the 169-foot 

 sandstone. This drill record shows the occurrence of the thin beds of 

 coal supposed to occur in the lower p-art of the Eogers section, but which 

 were not found where the section was measured. The Mesaverde forma- 

 tion at Eogers contains two groups of developed coal beds, the upper one 

 probably equivalent to the group described at Madrid and the lower one 

 to the coals at Omera and to the middle group shown in the 1,602-foot 

 drill record. These relations are best shown in figure 5. 



No fossil plants were found in the Mesaverde near Eogers, but oyster 

 shells, identified as Ostrea sp. related to 0. soleniscus Meek, were found 

 about half a mile south of the line along which the section was measured. 

 They occur in yellow concretions similar to those in the basal sandstone 

 of the Mesaverde which yielded Gastropods and other marine fossils indi- 

 cated in the section. They occur above a thin bed of coal about 50 feet 

 stratigraphically above the lowest coal observed at this locality. The 

 oyster shells are large and no complete ones could be found, but frag- 

 ments were obtained an inch or more in thickness and 10 inches longr. 



There is good evidence at Eogers of an unconformity between the Mesa- 



