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574 W. T. LEE STRATIGRAPHY OF COAL FIELDS OF KEW MEXICO 



made, with those west of the mountains, it was necessary to make collec- 

 tions from these three formations, as well as from the shale below the 

 Mesaverde. This was done in all of the coal fields visited, and care was 

 exercised to locate the collections as definitely as possible in measured 

 sections. 



Preliminary Statement of Results 



The stratigraphic succession of the formations and their relation to 

 each other were determined in each of the fields examined. The fossil 

 plants collected have been examined by F. H. Knowlton and the fossil 

 shells by T. W. Stanton. The correlations are based on the stratigraphic 

 sequence of the formations, on lithologic resemblances, and on the fossils. 

 Some of the proi)ositions advocated in this paper may be regarded as 

 essentially proved, others as fairly well sustained, while some are ad- 

 vanced only as working hypotheses. 



Among the propositions that are regarded as essentially proved are : 



(1) The thick shaale — the Mancos — ^l^elow the principal coal-bearing 

 formation in the southeastern part of the San Juan Basin is represented 

 by a shale of similar character and essentially equivalent age in each of 

 the smaller fields as far east as Galisteo. Although the top of this shale 

 varies slightly in age. from place to place, it represents a once continuous 

 formation extending from the San Juan Basin eastward to some un- 

 known distance beyond Galisteo. 



(2) The principal coal-bearing rocks of the San Juan Basin — the 

 Mesaverde formation — are represented by. similar rocks in each of the 

 smaller fields near the southern end of the Eock}^ Mountains, and 

 although both the upper and the lower limits of the formation may vary 

 somewhat in age from place to place, the coal-bearing rocks heretofore 

 known as Laramie in these smaller fields are of essentially the same age 

 as the Mesaverde of the San Juan Basin. 



Among the propositions which may be regarded as probably true, 

 although less well sustained than those noted above, are : 



(1) Tlie Mancos shale of the southeastern part of the San Juan 

 Basin is essentially equivalent in age to the shale originally described as 

 Mancos. 



(2) The Mesaverde formation of the southeastern part of the San 

 Juan Basin is lithologieally similar to the original Mesaverde, but is 

 thicker and may include rocks slightly younger than the typical Mesa- 

 verde. 



(3) The base of the Mesaverde of the Rio Puerco field, as represented 

 by the Punta de la Mesa sandstone, is several hundred feet lower in the 



