632 W. T. LEE STRATIGRAPHY OF COAL FIELDS OF NEW MEXICO 



and therefore older than the Hagan coals. In many places in the Tijeras 

 field the basal sandstone of the Mesaverde contains marine shells of spe- 

 cies identical with those found in the sandstone below the coal in the 

 Hagan field. Coal lies immediately above this sandstone, and associated 

 with it are fossil plants, but only a few poorly preserved specimens were 

 found. The Mesaverde of the Tijeras field is essentially a marine forma- 

 tion and shells were collected from it at several horizons, as indicated in 

 the section. 



There is a zone of shale and sandstone above the principal coal beds 

 which contains marine fossils and which may be the equivalent of the 

 Lewis shale of the southern part of the San Juan Basin described by 

 Gardner (116). It is somewhat thicker than the Lewis in the south- 

 eastern part of this basin, the locality nearest to the Tijeras field at 

 which the Lewis is known to occur. The fossils named in the accom- 

 panying section indicate clearly the marine character of these beds, and 

 if the Tijeras section were compared only with the sections measured in 

 the Hagan and Cerrillos fields to the north it would seem proper to cor- 

 relate the coal-bearing rocks with the coal measures of the Hagan and 

 Cerrillos sections and refer the marine beds above them to a higher hori- 

 zon not now represented in the Hagan and Cerrillos fields. On the other 

 hand, if the Tijeras section be compared with that of the Eio Puerco 

 field, it appears that the rocks containing these marine shells may repre- 

 sent one of the marine horizons known to occur within the Mesaverde in 

 that field. The fossil shells seem to favor the latter correlation, for they 

 are not characteristic Lewis species. They do not differ materially from 

 those found at several horizons within the Mesaverde, and because of this 

 fact these rocks are included in the Mesaverde. 



These marine beds are overlain by a coarse-grained, hard, cliff-making 

 sandstone, which differs in character and appearance from the sandstone 

 below to such an extent that it suggests the beginning of a new forma- 

 tion. This in turn is overlain by coal-bearing sandstone and shale. If 

 the underlying beds containing the fossils of marine origin prove to be 

 Lewis the higher beds may be regarded as Laramie. N"o fossils except a 

 few poorly preserved plants were found in them, and these proved to be 

 insufficient for the determination of age. These younger coal-bearing 

 rocks are confined to the trough in the center of the syncline and occupy 

 an area of only a few acres. Coal occurs near the base of the formation, 

 but the rocks intervening between it and the basal sandstone, which is 

 relatively hard, consist of soft sandstone and shale so poorly exposed that 

 the' thickness could not be measured. Two coal beds separated by an in- 

 terval of 25 feet are known to occur in this upper coal-bearing formation. 



