60 Shimer and Blodgett — Jit. Taylor Region, New Mexico. 



Ostrea lugubris Conrad 

 0. translucida M. and H. 



?0. sannionensis White 

 Caryates veta Whitfield 

 Pinna petrina White 

 Sphenodiscus lenticulare (Owen) 

 Buchiceras sioallovi (Shumard) 

 Placenticerus placenta (Dekav) 

 P. costata Herrick and Johnson 

 JExogyra Icevhiscida Koemer 

 JE. columbella Meek 

 Liopistha concentrica Stanton 



Camptonectes symmetricus Herrick and Johnson 

 Paculites gracilis Shumard 

 Prionotropis woolgari (Mantell) 



The strata vary in age from the Fort Benton at Great Neck 

 to doubtful Fort Pierre east of Cabezon ; this latter determi- 

 nation was made upon but one fossil, Astarte evansi. The 

 other faunas, especially those from Necks 14, 3 and from local- 

 ity B show a commingling of many specimens of the Colorado 

 formation with a few of the Montana. This would apparently 

 indicate an upper Fort Benton age for the beds, unless we sup- 

 pose that the apparent absence of clear water in this region 

 during Niobrara times would cause the absence of the typical 

 Niobrara fauna and the persistence of the Fort Benton fauna 

 to Montana times. Under such a supposition, some of these 

 intermediate strata would represent the Niobrara time, with- 

 out the presence of the typical Niobrara fauna. 



The strata where penetrated by the igneous rocks (dikes, 

 necks, etc.) maintain their normal dip even up to contact with 

 the igneous rock, nor do they show much more jointing near such 

 contact than away from it. The baking of these sanely shales 

 is comparatively slight. At Neck 4, south of Salazar, con- 

 tact metamorphism is shown for only three feet from the 

 narrow igneous intrusion. At Neck 5 an excellent contact is 

 seen on the western side. The shales are here baked black for 

 10 feet ; for the next 15 feet the baking is slight, the shales 

 being darker than the unaltered beds, while beyond 25 or 30 

 feet the strata are practically unchanged. 



Description of Species. 



Mollusca. 

 Pelecypoda. 

 Ostrea lugubris Conrad. 



(Bull. U. S. G. S. 106, p. 48.) 

 Agrees with description in size, general shape, and in plica- 

 tions and concentric lines. 



