2IO SMITHSONIAN MISCEI.LANEOUS COLLECTIONS VOL. 53 



STEPHEN FORMATION (continued): 

 I (continued) : 



Nisusia alberta (Walcott) [1889, p. 442], van 

 Hyoiithes carinatus Matthew [1899, p. 42]. 

 Agnostus sp. 

 Agraidos sp. 

 Menocephalns sp. 

 Ptychoparia, 3 species. 

 Neolenus sp. 

 Bathyuriscus sp. 



At Mount Stephen, about seven miles southwest of Mount Bosworth, a 

 siliceous shale occurs at the summit of the Stephen formation in which an 

 unusually rich fauna occurs. This shale is not well developed on Mount 

 Bosworth. 



Ogygopsis Shale;. — This term is applied to the local development of arena- 

 ceous and calcareous shale at the summit of the Stephen formation on the 

 northwest slope of Mount Stephen. The shale band (lentile) has a maximum 

 thickness of about 150 feet. It thins out to the northeast and is faulted out to 

 the southwest. At its maximum thickness, 2,800 feet above Field, it carries 

 immense numbers of trilobites, especially Ogygopsis klotzi (Rominger), 

 Bathyuriscus rotundatus (Rominger), Neolenus serratus (Rominger), Zacan- 

 thoides spinosus (Walcott), and, in addition, sponges, cystids, brachiopods, 

 pteropods, and gasteropods. The shale is less rich in fossils one-fourth of a 

 mile northeast on the strike ; also to the northwest. Lentiles of gray quartzitic 

 sandstone and siliceous, gray limestone occur in the shale, and the entire shale 

 band appears to be a lentile between the thin-bedded blue limestones and the 

 superjacent massive, arenaceous limestone formation. There is no trace of 

 the Ogygopsis shale on Mount Bosworth 6 miles northeast, at the same 

 horizon, or at Castle Mountain, 20 miles east-southeast. 



There is a sharp anticline, with a northeast-southwest axis, in the shale and 

 the thin-bedded limestones beneath, on the northwest slope of Mount Stephen. 

 The southeast limb is crushed and the beds are largely faulted out against the 

 massive arenaceous limestone before reaching the amphitheater at the head of 

 Field Brook. On the northwest limb the shales are unaltered and slope down 

 the side of the mountain for 1,800 feet, thus affording a great exposure of the 

 shale and contained fossils. 

 Fauna: 



1. Hyolithcllus Uagellum (Matthew) [1899, P- 4o]. 



2. Hyolithellus annulatus (Matthew) [1899, p. 42]. 



3. Orthotheca corrugata Matthew [1899, p. 42]. 



4. Orthotheca major Walcott [i9o8r, p. 246, pi. I, fig. 11]. 



5. Hyoiithes, sp. 



6. Hyoiithes carinatus Matthew [1899, p. 42]. 



7. Stenotheca zvheeleri Walcott [i9o8r, p. 245, pi I, fig. 7]. 



8. Platyceras romingeri Walcott [1889, p. 442]. 



9. Platyceras hdlianus Walcott [i9o8r, p. 246, pi. I, fig. 13]. 



10. Acrofreta dcpressa (Walcott) [1889, p. 441]. 



11. Micromitra (Iphidella) pannula (White) [1874, p. 6]. 



12. Obolus mcconnclli (Walcott) [1889, p. 441]. 



13. Nisusia alberta Walcott [1889, p. 442]. 



14. Philhedra columbiana (Walcott) [1889, p. 441]. 



