366 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 75 



The photographs of Robson Peak indicate the presence of a dark 

 band that may represent the dark limestones of BilHngs Butte "with 

 their Lower Ozarkian fauna. The place to work this problem out is 

 probably in the ridges east of Moose Pass where there are fine ex- 

 posures of the limestones above the Middle and Upper Cambrian. 

 I did not realize this until it was too late to return in 1913 (see pi. 100) . 



The above statements are based on our present information, and are 

 subject to correction when a competent geological survey is made. 



Iyatunga Mountain Section 



L. D. Burling's section of Iyatunga (Rearguard) Mountain (see 

 pi. 95), measured in 1917, is an important contribution to the strati- 

 graphic section of the Robson District, as it includes in an unbroken 

 series nearly 3,000 feet (914.4 m.) of Upper Cambrian strata and 

 875 feet (266.7 ni-) of the superjacent Chushina formation of the 

 Ozarkian. At the base of the section, in 2, the few fossils found by 

 me in 1912 and those found by Burling in 1917 may be referred 

 to the Upper Cambrian, but they are near the base, and the topography 

 where Hunga glacier sweeps around the base of Iyatunga indicates 

 readily eroded rocks beneath, of the character of the shales at the 

 base of the Upper Cambrian Lynx formation at Snowbird Pass. I 

 have added 500 feet (152.4 m.) to this part of the section as an 

 estimate for the shaly and arenaceous beds at the base of the Lynx in 

 the Titkana Peak and Chushina Ridge section of the Upper Cambrian 

 that are not exposed in the Iyatunga section. 



The section was measured by Burling when in the service of the 

 Geological Survey of Canada, and is used by permission of the Direc- 

 tor of the Survey. The Burling fossils were received from the Survey 

 by the United States National Museum largely as they were packed 

 in the field, and after being partially prepared, were studied and 

 provisionally identified. 



OZARKIAN 



Chushina Formation (At the summit of mountain) 



* Feet Meters 



la. Shales with interbedded limestones, and near top, rusty 



brown nodules 75 22.9 



(top of 29 of Burling's field section). 



Fauna. — (17-130) : Kainella fauna of Billings Butte (Ex- 

 tinguisher). See Walcott's section, p. 358. 



ih. Series of thin-bedded greenish shales, with bands of 

 limestone and intraformational conglomerate (29 of 

 section) 200 -f- 61.0 -f- 



ic. Massive, blue, clifif-forming limestone (28 of section) . . 100 30.4 



