DETAILED STRATIGEAPHIC DISTEIBUTION. 



127 



Detailed stratigraphic distribution of Cambrian and Ordovician Brachiopoda — Continued. 

 British Columbia: Mount Bosworth— Continued. 



a This is the locality containing the beautifully preserved annelids, medusa, holothurian?, crustaceans, etc., now being described and illus- 

 trated in volume 57 of the Smithsonian Miscellaneous Collections. 



i> The name Ogygopsis zone is applied to the local development of arenaceous and calcareous shale at the summit of the Stephen formation on the 

 northwestslope of Mount Stephen. The shale band (lentile) has a maximum thickness of about 150 feet. It thins out to the northeast and is faulted 

 outto thesouthwest. At its maximum thickness, 2,800 feet above Field, it carries immense numbers of trilobites, especially Ogygopsis klotzi (Rom- 

 inger), Sai/i?/tirisctts rotundatus (Rominger), Neolenus serratus (Rominger), Zacanthoides spinosus (Walcott), and, in addition, sponges, cystids, 

 brachiopodSjpteropods, and gastropods. The shale is less rich in fossils one-fourth mile northeast on the strike; also to the northwest. Lentiles 

 ofgrayquartzitic sandstone and siliceous gray limestone occur in the shale, and the entire 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 zone at the same horizon on Castle 

 Mountain 20 miles east-southeast. On Mount Field It is represented by the Burgess shale, Locality 35k. 



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,S00 feet, 

 thus affording a great exposure of the shale and contained fossils. 



