DESCRIPTIVE DETAILS I CERRILLOS FIELD 653 



The variegated sandstone and shale at the base of the section has been 

 referred to the Morrison on lithologic and stratigraphic grounds. No 

 fossils have been found in it in this region. The lower part, 200 feet or 

 more in thickness, consists of soft shale and friable sandstone of many 

 shades of color. This character has been noted in so many places that it 

 has come to be regarded as more or less diagnostic of the Morrison forma- 

 tion. Above these softer beds is a coarse conglomerate 10 feet thick over- 

 lain by 80 feet of variegated sandstone and shale. Were it not for the 

 color of the beds above it this conglomerate might be regarded as the 

 base of the Dakota. However, although conglomerate is rare in the Mor- 

 rison the reference of the 10-foot conglomerate to this formation seems 

 inevitable; also the overlying thin-bedded sandstone, although white, 

 probably belongs in the Morrison. Between it and the overlying con- 

 glomerate, which is here referred to the Dakota, there is an uneven line 

 of separation more or less conspicuous wiiich may mark an unconformity. 

 The writer has formerly shown (112, page 18) that in the Galisteo 

 Canyon the Morrison apparently lies unconformably on the Yeso forma- 

 tion. It seems probable therefore that the Morrison in this region is 

 separated in time from both underlying and overlying formations. 



Above the rocks here referred to the Morrison is a sandstone about 

 50 feet thick, conglomeratic near the base and otherwise similar in char- 

 acter and appearance to the Dakota sandstone throughout the southern 

 Eocky Mountain region. No fossils were found in it^ and its reference 

 to the Dakota is based on its lithology and stratigraphic position. 



Carbonaceous shale in which coal occurs in some places was found 

 above the Dakota sandstone. The shale and coal are both irregular in 

 thickness and character. The coal was observed in several places and 

 found to vary in thickness from a mere film to about 6 inches. There is 

 a conglomerate above the coal which also varies in thickness and character 

 and is absent in some places. Apparently this carbonaceous shale, coal, 

 and conglomerate belong in the Mancos shale formation and are not to be 

 included in the Dakota. The only place at this locality where a line of 

 separation can rationally be drawn between the Dakota sandstone and 

 the Mancos shale is at the base of the carbonaceous shale, where there is 

 an abrupt change from the shale to the quartzose sandstone below it. On 

 the other hand, there is a tendency on the part of some observers of 

 Rocky Mountain geology to call any coal near this horizon "Dakota coal," 

 and it is probable that although this coal in the Galisteo region clearly 

 lies above the base of the Mancos shale it may be the equivalent in age of 

 some of the so-called Dakota coal of the southcM'n Tiockv ^lountain rcirion. 

 An attempt was made to find the coal at other localities in the Cerrillos 



