358 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 75 



Lower Cambrian sandstones come in contact with the pre-Cambrian on 

 the ridge above Rainbow Brook (Lake Kinney Station [6,849 ^^^^' 

 2,087.6 m.] of Wheeler map). About midway of the lake, the green- 

 ish and gray shales and limestones above the sandstones dip 20° north- 

 east into the mountain. 



On the west and northwest side of Robson Peak, south of Emperor 

 Falls, the limestones dip 10° east into the mountain. Looking south 

 from the high ridge northwest of Berg Lake, the Robson massif has 

 a broadly synclinal structure (see pi. 99, where it is partially shown), 

 and on the northeastern side the dip is southwest and west into the 

 mountain (see pi. 94). 



Stratigrapiiic Section * 



With the information now available it is possible arbitrarily to 

 divide the Robson limestones of the 1913 section into an upper series, 

 for which the name Robson is retained, and a lower series 1,500 feet 

 (457.2 m.) thick, which is characterized by the distinctive fauna 

 of the Ozarkian Chushina ' formation, the upper series being ten- 

 tatively referred to the Ordovician. 



In 1913 I referred both the upper and lower series of the Robson 

 limestones to the Ordovician, saying : 



The upper 1,500 feet [457.2 m.] of Robson Peak is practically inaccessible. 

 The limestones appear to be more massive-bedded and arenaceous than the 

 strata below. They weather like the great arenaceous limestones of the Kicking 

 Horse Pass section 150 miles [241.3 km.] to the south. Large blocks of the 

 arenaceous and dolomitic buff-weathering limestone, also siliceous and cal- 

 careous gray shale with buff- weathering magnesian limestone in thin layers, 

 were brought down from high up on Mount Robson by the central moraine 

 of Hunga glacier. 



The section is now modified as follows : 



ORDOVICIAN ? 

 RoBSON Formation „ , ,, , 



rcet Meters 



Partly siliceous, arenaceous and dolomitic gray and buff 

 limestones in layers varj-ing from one inch to 18 inches 

 (2.5 to 45.7 cm.) in thickness. (Estimate) 500 152.4 



Fauna. — None found, as strata were inaccessible for col- 

 lecting. 



OZARKIAN 

 Chushina Formation 



I. Thin-bedded, gray limestones with intcrbeddcd bands 



of shale. (Estimated) 1,500 457-2 



* Smithsonian Misc. Coll., Vol. 57, No. 12, 1913, pp. 336-341. 

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



