PREVIOUS INVESTIGATIOiSrS 583 



in form for publication. The greater part of the evidence of age is de- 

 rived from fossil plants which are being studied by Dr. F. H. Knowlton. 

 Although his study of them is by no means complete, it has progressed 

 far enough to indicate that, in his opinion, the plants of the upper for- 

 mation are undoubtedly of post-Laramie age, and tluit those of the k)\ver 

 formation are older than recognized Laramie. 



During the summer of 1911 the writer carried on the investigations 

 described in this paper in an attempt to correlate the formations of the 

 Eaton Mesa region with those of the coal fields south and west of the 

 Eocky Mountains. A preliminary statement of results was given at the 

 Washington meeting of the Geological Society of America, in which it 

 was shown that the evidence derived from the study of stratigraphy, of 

 fossil plants, and of fossil shells all agree in correlating the coal beds 

 of the Cerrillos, Hagan, and Eio Puerco coal fields with the Mesaverde 

 formation of the southeastern part of the San Juan Basin, and that tlie 

 fossil plants associated with these coal beds are essentially the same as 

 those found in the coal-bearing formation below the unconformity in the 

 Eaton Mesa region. 



After the present paper wa^ in type, but before it went to press, the 

 writer, in company with T. W. Stanton, made some examinations in the 

 Eio Puerco field and along the eastern margin of the San Juan Basin 

 from Cabezon to Monero, principally for the purpose of determining the 

 relations of the coal -bearing rocks in the southeastern part of the San 

 Juan Basin to the typical Mesaverde in tlie northern part of this basin. 

 The results of this work cannot be embodied in the present paper, but it 

 may be briefly stated (1) that at least the lower part of the coal-bearing 

 rocks at Cabezon is essentially equivalent to the Mesaverde as represented 

 at Monero, which in turn is the undoubted equivalent of the original 

 Mesaverde, and (2) that these same rocks seem to be equivalent in age 

 to the middle and upper portions of the coal-bearing rocks in the Eio 

 Puerco field : in other words, that the base of the Mesaverde in the Eio 

 Puerco field, as rej^resented by the Punta de la ^lesa sandstone, is lower 

 in the section by several hundred feet than the base farther north, and 

 that these several hundred feet of sandstone and sandy shale are equiva- 

 lent in age to the upper part of the Mancos near Cabezon. 



Geologic Formations 

 the type section 



In 1899 Whitman Cross (75) published a section of the Cretaceous 

 rocks that has become the standard for southwestern Colorado and west- 

 ern Xew Mexico. This section divides the Cretaceous into Dakota sand- 



