368 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 75 



lake as extended beneath the peak. This gives approximately a little 

 over 6,000 feet (1,828.8 m.) in thickness for the strata exposed in 

 Titkana Peak, from its northwest base to the summit north-northwest 

 of Snowbird Pass. My section of 1912 for the same series was 6,200 

 feet (1,889.8 m.) as measured and estimated. This includes the 

 Chetang, Tatei, and Titkana formations of the Middle Cambrian. 

 From the top of Titkana Peak south, the strata are of the character 

 of the beds at the base of the Upper Cambrian in the Mount Bosworth 

 section,^ where a series of ripple-marked, mud-cracked, arenaceous 

 shales 268 feet (81.7 m.) thick occur at the base of the Upper Cam- 

 brian limestones. Burling's field notes indicate that he found a some- 

 what similar series of shales with interbedded thin layers of limestone 

 extending from the south slope of Titkana Peak to Snowbird Pass 

 and up the north slope of Chushina Ridge (see pi. 105) to its 

 summit, the section measuring 449 feet (136.9 m.) in thickness. These 

 shales of shallow, and probably brackish water origin, form the base 

 of the Upper Cambrian Lynx formation in the Robson District, and 

 also occur at a similar horizon in the Ranger Canyon section of the 

 Sawback Range (see p. 264). Burling also measured a disconnected 

 series of strata somewhat similar to that of the Lynx in a saddle west 

 of Lynx Mountain, that apparently has no direct stratigraphic con- 

 nection with the Snowbird Pass-Chushina section, and cannot, with 

 the data available, be correlated with it. This section was probably 

 seen up among the snow fields shown about Lynx Peak in plate 84. 



The Robson District section is subject to a thorough revision. Much 

 more work should be done on it, as my reconnaissance of 191 2 and 

 1913, and Burling's work of 1915, 1917, are very inadequate. 



^ Smithsonian Misc. Coll., Vol. 53, No. 5, 1908, p. 208. 



