582 W. T. LEE STRATIGRArilY OF COAL FIELDS OF NEW MEXICO 



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are described as "Upper Montana — relation to the Mesaverde unknown 

 This was followed in 1907 with a i^aper by Slialer (105), who traced the 

 formations of southwestern Colorado around the western margin of the 

 San Juan Basin. 



In 1908 a paper was published by Shimer and Blodgett (109) which 

 aids materially in correlating the coal measures of the Eio Puerco field 

 with those of the San Juan Basin. These observers collected fossils at 

 several localities between the two coal fields from the fossil-bearing zones 

 that had been described by Herrick and Johnson as occurring in the 

 shale below the coal beds of the Rio Puerco field. 



A year later, 1909, Gardner (110) referred Schrader's "Upper Mon- 

 tana group" of tlie southeastern part of the San Juan Basin to the 

 Mesaverde and found the Lewis shale and the "Laramie" coal beds 

 higher in the section. This was followed by two papers from the same 

 writer (116 and 117) in which these correlations were strengthened. 



In 1905 the present writer began making observations in Xew Mexico, 

 and in the following year (97) announced the discovery of bones of 

 Triceratops in rocks younger than the coal measures near Engle, Xew 

 Mexico, about 150 miles south of the area described in the present paper. 

 These rocks have a conspicuous basal conglomerate that was later found 

 to lie unconformably on the coal-bearing rocks.* In this and in a later 

 paper (104) these rocks were provisionally correlated M'ith the Galisteo 

 sandstone of the Cerrillos coal field, and there in turn with the post-Lara- 

 mie beds found elsewhere, which were at that time and still are by some 

 geologists regarded as being of late Cretaceous age. The next step taken 

 by the writer in this study was in 1908, when he discovered an uncon- 

 formity announced in 1911 (111) in the Raton coal field of New Mexico. 

 The coal-bearing rocks previously referred to the Laramie were found to 

 be separated by this unconformity into two formations, the upper one of 

 which was correlated on fossil evidence with the post-La ramie rocks of 

 the Denver Basin, while the lower one contains a flora that is regarded 

 as older than Laramie. In 1910 the writer, assisted by J. B. Mertie, 

 spent the field season in tracing the coal-bearing formations around the 

 Raton and Trinidad coal fields and in studying their relations to each 

 other and to neighboring formations. A preliminary announcement of 

 results was made (119), in which it was shown that the unconformity is 

 readily traceable in all parts of these two fields. A large amount of evi- 

 deiu^e was collected bearing on the structural relations and the geologic 

 age of these two coal-bearing formations, but the information is not yet 



* Personal communication from Mr. Max W. Ball. 



