642 W. T. LEE STRATIGRAPHY OP COAL FIELDS OF NEW MEXICO 



lowish brown color and contains fossiliferous concretions of impure lime- 

 stone. No coal or carbonaceous shale was found below the sandstone that 

 is here regarded as the base of the Mesaverde. The sandy shale is re- 

 garded as the transitional zone at the top of the Mancos, although it is 

 quite possible it may be the equivalent in time of the lower part of the 

 Mesaverde of other localities. 



At the base of the measured section occurs a massive sandstone that 

 appears to be at the same horizon as that at the base of the Mesaverde at 

 Hagan. Five coal beds exposed in the mine entries, now abandoned, and 

 several prospect openings were observed above this massive sandstone. 

 The coals apparently hold the same position as those previously described 

 from the Sloan and Hagan mines. Fossil plants were found at several 

 horizons closely associated with the coal beds and several were collected 

 principally from the sandstone and shale overlying the main coal bed. 

 They are named as lot number 6028 in the accompanying section. 



There is a series of shales and sandstones above the coal-bearing rocks 

 containing ironstone concretions. These rocks may be the time equiva- 

 lent of the rocks constituting the highest shaly member of the Mesaverde 

 at Hagan. On them, as at Hagan, a conglomerate rests unconformably. 

 It is the basal conglomerate of the colored rocks which are correlated in 

 a general way with the Galisteo sandstone of the Cerrillos field. They 

 contain great numbers of petrified logs, some of them very large. The 

 state of preservation of most of them is poor and no specific determina- 

 tions have been made. No identifiable fossils have been found in these 

 colored rocks and their geologic age is not definitely known. 



The coarse conglomerate which overlies the colored beds is composed 

 principally of igneous material derived from the Ortiz Mountains. It 

 consists of angular blocks of igneous rock varying in diameter from a 

 few inches to several feet. The material is irregularly bedded and the 

 beds dip eastward by about the same degree (30 degrees) as the underly- 

 ing rocks. The thickness obtained by correcting for dip the distances 

 measured across the strike in the upper part of the gulch, locally known 

 as Devils Canyon, is about 3,000 feet, but this may be in excess of the 

 actual thickness, for the bedding is too irregular to admit of accurate 

 determinations of thickness. It is certain, however, that this conglomerate 

 is many hundreds of feet in thickness. It is the same as the youngest 

 conglomerate of the Hagan section that was described as lying uncon- 

 formably on the- Galisteo (?), Mesaverde, and Mancos formations. 



CERRILLOS FIELD 



The Cerrillos coal field is better known than those just described, 

 mainly because of the productive mines which have been operated here 



