DESCRIPTIVE DETAILS: CABEZON 619 



"I have carried a reconnaissance survey around the north side of the San 

 Juan Basin and have done the details of the Ignacio folio which lies to the 

 west but on the rim of the same basin. There is no doubt in my mind, based 

 on reconnaissance mapping and lithological similarity, that the beds to which 

 you refer (those above the unconformity) are Animas. . . . The heavy 

 conglomerate beds at the base of the Animas are in the form of a lentil which 

 thins out away from the Animas Valley. The beds above this consist of tan- 

 colored and greenish shale alternating with coarse-grained, tan-colored sand- 

 stone containing grains of igneous origin. . . . The beds which are intruded 

 with sills along the canyon and cross-cut by dikes (the upper 461 feet of the 

 foregoing section) are of the same nature and apparently connect with the 

 upper beds of the Animas. They are older than the Puerco and Torrejon, 

 and contain remains of Triceratops." 



CABEZON 



The writer made few observations between Dulce and Cabezon, a dis- 

 tance of about 90 miles. Doctor Gardner (116) correlated the rock for- 

 mations exposed near Cabezon with those of the Durango region and gave 

 them the same names, namely, Mancos, Mesaverde, Lewis, and "Lara- 

 mie." The correlation is based on the work of tracing the outcrops of 

 these formations around the San Juan Basin from their type locality in 

 southwest Colorado. They are described as more or less continuously 

 exposed on the west and south sides of the basin, but for a short distance 

 west of Nacimienta Mountains they are covered by overlapping Tertiary 

 rocks. However, in spite of the great length of outcrop around the basin 

 to the west and the area of obscured outcrops on the east side. Doctor 

 Gardner seems to have felt confident that the formations near Cabezon 

 are to be correlated directly with those of the Durango section. He col- 

 lected fossils from both the Lewis shale and the Mesaverde formations. 

 They are among the LTnited States Geological Survey collections and 

 have been identified by T. W. Stanton. Two collections were obtained 

 from the Lewis as follows: 



Invertebrates collected by J. H. Gardner from ahout 100 Feet below the Top of 

 the Lewis Shale about 6 Miles Southeast of Raton Spring, 'New Mexico 



(United States Geological Survey locality number 4455) 



Ostrea sp. Liopistha undata M. & H. 



Cardium speciosum M. & H. Lunatia sp. 



Legumen sp. Melam^ia? sp. 



Invertebrates collected from the Lewis Shale by J. H. Gardner two and one- 

 half Miles Southeast of Cuba, New Mexico 



(United States Geological Survey locality number 4452) 



Inoceramns barabini Morton Placenticeras intercalare M. & H. 



Baculites compressus Say 



XLIV— Bull. Geol. Soc. Am., Vol. 23, 1911 



