no. 5 pre-de\'onian paleozoic formations 245 



Lynx Formation. Walcott, 1913* 



Type locality. — Chushina Ridge from Snowbird Pass to Lynx 

 Mountain ; also on lyatunga, Robson Peak District. 



Derivation. — From Lynx Mountain. 



Character. — Thin-bedded, bluish-gray limestones with alternating 

 bands of calcareous light gray shale. 



Thickness. — Measured on lyatunga Mountain (Burling), 2,765 feet 

 (842.8 m.). 



Geographic distribution. — Not known outside of the Robson massif, 

 but it probably extends to the north and south and also east and 

 southeast of Moose Pass in the Tokana Mountains. 



Fauna. — Upper Cambrian apparently to be correlated with the 

 Lyell formation. 



At the base a thick band (200 feet, 60.9 m.) of gray, greenish, 

 and reddish-brown siliceous and arenaceous shales, containing mud 

 cracks and ripple marks, would appear to represent the Arctomys. 



Arctomys Formation. Walcott, 1919' 



Type locality. — South slopes of Sullivan and Survey Peaks on the 

 north side of Glacier Lake (pi. 26 at B). 



Derivation of name. — From Arctomys Peak situated a short distance 

 northwest of the type locality. 



Character. — Finely laminated, smooth-surfaced limestones over- 

 lying siliceous, arenaceous, and calcareous shales and interbedded 

 laminated limestones ; the entire formation at Glacier Lake conveys 

 the impression that it was a deposit of fine silts, sands, and calcareous 

 muds or slimes in a shallow sea that marked the beginning of the 

 Upper Cambrian in the Cordilleran Geosyncline in this area. At 

 Mount Bosworth, Ranger Brook Canyon, and Cotton Grass Cirque, 

 ripple marks, mud cracks, and casts of salt crystals occur on the hard, 

 finely arenaceous, shaly layers. 



The formation appears to represent the period of deposition of a 

 series of shallow fresh-water deposits, 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 low, old land surfaces. These fine shales and sandstones alter- 

 nate with more or less thin, calcareous and arenaceous layers and have 

 on their surfaces ripple marks, mud cracks, and casts of salt crystals. 

 They re])resent, in the Bow Valley area, the period of transition from 



^ Smithsonian Misc. Coll., Vol. 57, No. 12, 1913, p. 334. 

 ' Idem, Vol. 67, No. 8, p. 461. 



