Shinier and Blodgett — Mt. Taylor Region, New Mexico. 59 



Of these fossils the following are cited by Stanton* as not 

 ranging above the Colorado : Gryphcea newberryi, Inocera- 

 mus labiatus, I. dimidius. Ostrea lugubris, Gardium, pau- 

 2?erculum / this is also true of the genus Prionotropis, while 

 P. woolgari is characteristic of the Fort Benton. Yoldia sub- 

 elliptiea and Anomia propatoris are characteristic of the Pug- 

 nellus sandstone (upper Fort Benton) in Colorado. Lunatia 

 eoncinna occurs in the upper Kanab valley in Utah associated 

 with a Colorado fauna. Ostrea anomioides var. nanus has been 

 found only in the Fort Pierre of the Cerrillos Hills, New 

 Mexico, f 



Thus all except the last indicate a Colorado age for the 

 strata, while the presence of this last variety and the forms 

 characteristic of the Piignellns sandstone give it a late Fort 

 Benton aspect. 



Summary. 



The area under consideration is near the central part of 

 New Mexico and is mapped on the eastern edge of the Mt. 

 Taylor sheet and the southwestern and northwestern corners 

 respectively of the Jemez and Albuquerque sheets. The road 

 traveled followed up the Puerco river valley, on the western 

 side of the Prieta mesa, as far as the village of Cabezon, thence 

 bending southeast down the eastern side of the mesa. 



A well-marked zone bearing calcareous septaria was observed 

 along the western side of the mesa from the base of Great 

 Neck near contour line 6500, north to Salazar at contour line 

 5800, where it disappears from view beneath the old flood 

 plain of the Rio Puerco. 



The fossils collected from this zone show the strata to be of 

 Colorado age, probably of the Fort Benton. 



A fossiliferous zone likewise characterized by septaria sim- 

 ilar to those on the western side of the Prieta mesa was noted 

 on the northeastern side. The fauna, however, is entirely dif- 

 ferent from that on the opposite side and the beds were found 

 at an altitude 300 feet higher than that southwest of Salazar, — 

 a difference too great to be offset by the slight westerly dip. 



Hence it is evident that at least two septaria zones are pres- 

 ent in the Cretaceous strata of the Puerco valley, though in 

 no one place were two such zones noted even in sections of a 

 thousand feet. Evidence of still another such zone is sug- 

 gested in the almost totally distinct fauna of the "cephalopod 

 zone" mentioned by Herrick and Johnson as occurring on the 

 southwest corner of the Albuquerque sheet. Their faunal list 

 is as follows : 



*U. S. G. S. Bull. 106, p. 48. 



fD. W. Johnson, Geology of the Cerrillos Hills, New Mexico School of 

 Mines Quart. 1908, Jan. -Oct. 



