226 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL 75 



limestone. The lower boundary in the Glacier Lake section is at the 

 base of a massive band of gray limestone 740 feet (225.6 m.) thick, 

 beneath which the fossiliferous shales and thin layers of interbedded 

 limestones of the Sabine formation occur. At Section Mountain on 

 the north side of the Upper Clearwater Canyon (E on map), the 

 Mons is superjacent to a dolomitic limestone, that is referred to the 

 Lyell formation, the Sabine formation with its characteristic fossils 

 being absent. The base of the Mons is more or less concealed in the 

 Fossil Mountain-Oyster Peak section, but a mile to the south at 

 Tilted Mountain Brook, there is a band of magnesian limestone 130 

 feet (39.6 m.) thick below the base of the Mons shales that is referred 

 to the Sabine formation, which here has a thickness of 415 feet 

 (125.6 m.) and contains several Upper Cambrian faunules. 



Chushina Formation. Walcott. 1923' 



Type locnUty. — Northwest slope of Chushina Ridge, above Snow- 

 bird Pass, and north base of Lynx Mountain above Hunga glacier, 

 and at Billings Butte (Extinguisher). 



Derivation. — From Chushina glacier and Ridge (see pis. 94, 105). 



Character. — Hard, dark gray limestones in thick layers that break 

 down into thin layers on weathering. Interbedded bands of calcareous 

 shale occur at several horizons. 



Thickness. — Estimated at 1,500 feet (457.2 m.), but this is prob- 

 ably too small. 



Geographic distribution. — Robson Peak massif and probably east 

 of Moose Pass. Ice and snow make it difficult of access, and not 

 until the section is studied east of Moose Pass is there much hope 

 of knowing the exact limits or characters of the formation. 



Fauna. — The Kainella fauna occurs in the limestone of Billings 

 Butte and on the summit of lyatunga Mountain (Rearguard), hence 

 this formation is equivalent to a portion of the Mons. 



Observations. — The base of the Chushina is clearly defined on lya- 

 tunga Mountain but the upper boundary is arbitrarily assumed to be 

 1,500-1- feet (457.2-1- m.) above, although it has not been worked out 

 either stratigraphically or by paleontological evidence. 



UPPER CAMBRIAN 



The Upper Cambrian formations may be grouped by their geo- 

 graphic distribution and character in two rather distinct regions — 



^ Smithsonian Misc. Coll., Vol. 67, No. 8, 1923, p. 458. 



