DESCRIPTIVE DETAILS : HAGAN FIELD 639 



several thin beds of coal. These beds have been prospected, but no place 

 was observed where the coal is more than a few inches thick, although a 

 considerable amount of carbonaceous shale was seen. 



The measured thickness of 600 feet is probably more than the normal 

 thickness of this shale. The measurement was made across the trough 

 of a tilted syncline and it is possible that the shale has been mechanically 

 thickened. It is not so well exposed and no measurement of its thickness 

 was made farther north, although the interval occupied by it was esti- 

 mated at considerably less than 600 feet. The rocks at Pina Vititos, 

 which probably represent this shale, were measured as 460 feet thick. 



Lying unconformably on these highest coal-bearing rocks is a con- 

 glomerate that constitutes the base of an extensive series of rocks younger 

 than the Mesaverde. These rocks are highly colored and consist of shale, 

 sandstone, and conglomerate similar in many ways to the Galisteo sand- 

 stone of the Cerrillos coal field, although they differ from the typical 

 Galisteo in being much more shaly; also the conglomerates consist of 

 well rounded pebbles of hard rock, whereas those of the Galisteo sand- 

 stone near Cerrillos contain many angular ones and slightly worn blocks 

 of relatively soft rock. However, it should be noted in this con- 

 nection that the pebbles of the lowest conglomerates near Cerrillos are 

 similar to those in the Hagan field, and that larger and more angular 

 ones are most numerous toward the top of the formation. On the other 

 hand, these colored rocks in the Hagan field are very similar in composi- 

 tion, color, and general appearance to the Tertiary rocks of the Rio 

 Puerco field, 30 miles to the west, and hold the same stratigraphic posi- 

 tion. Although it seems probable that these rocks will eventually prove 

 to be the time equivalents of some of the Tertiary formations of the San 

 Juan River region farther west, they are provisionally correlated with 

 the Galisteo sandstone formation. No fossils except petrified wood were 

 found in them. This occurs in the formation at all horizons in the form 

 of tree trunks 1 to 5 feet or more in diameter, and many well worn 

 pebbles of petrified wood, probably derived from tree trunks that were 

 embedded in the eroded portions of the underlying coal measures, were 

 found in the conglomerates. 



The youngest rocks near Hagan are coarsely conglomeratic and lie 

 with conspicuous angular unconformity on the eroded edges of the Galis- 

 teo (?) red beds northeast of Hagan, on the Mesaverde near Hagan, and 

 on the Mancos shale and the Manzano (Pennsylvanian) red beds farther 

 to the south. They consist principally of blocks of igneous rock derived 

 in recent geologic time mainly from the Ortiz Mountains and constitute 

 part of the formation which in the Cerrillos region was referred by John- 



