346 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL JK, 



Feet Meters 



cretions weathering buff, and 2 to 3 mm. in diameter, 

 are abundant, and small fragments of trilobites 



occur throughout 18 5.4 



l^. Massive-bedded, bluish-gray, dark limestone, with thin 



stringers of buff-weathering magnesian limestone.. .. 2i7 H-i 



Fauna. — Near base (64b) : 



Lmgulella sp. 



Oboliis sp. 



Crepicephalus sp. 



Coosia sp. 



Kingstonia sp. 

 Thirty feet (9.1 m.) above (64b), dark, round, con- 

 cretionary-like balls occur in profusion throughout a 

 layer 5 feet (1.5 m.) thick. Above the concretionary 

 layer, a layer 14 inches (35.5 cm.) thick of gray to 

 dove-colored limestone contains a small and peculiar 

 new fauna (64c) : 



Crepicephalus sp. 



Kingstonia sp. 



Arctomys Formation 



The Arctomys formation appears to represent the period 

 of deposition of a series of shallow, fresh-water de- 

 posits alternating with brackish-water and marine 

 sediments such as would occur in a shallow sea near 

 the mouth of a large river, bringing fine sand, mud, 

 and slimes derived from glacial streams originating 

 some distance from the shore line. These fine shales 

 and sandstones alternate with more or less thin cal- 

 careous and arenaceous layers and have on their sur- 

 faces ripple marks, mud cracks, and casts of salt crys- 

 tals. They represent, in the Bow Valley area, the 

 period of transition from the massive Middle Cam- 

 brian Eldon limestone beneath to the magnesian lime- 

 stones of the Upper Cambrian Bosworth formation 

 above. At Glacier Lake, the Eldon is absent by non- 

 deposition and the Arctomys is immediately super- 

 jacent to the Murchison limestones that represent the 

 Middle Cambrian Stephen formation of the Bow 

 Valley section. The shales and limestones of the Sulli- 

 van formation above the Arctomys are unlike the 

 thick-bedded limestones of the Bosworth formation 

 of the Kicking Horse-Bow Valley section (see p. 308). 



10. Bluish-gray, irregularly laminated limestone. The lamel- 

 lae are from .25 to 1.5 inches (.6 to 3.8 cm.) thick 

 and alternate as buff-weathering magnesian and blu- 

 ish gray limestone weathering light gray. The lami- 

 nations disappear in some of the massive layers, which 

 are a more or less thick-bedded, magnesian limestone. 520 158.5 



