NO. 12 CAMBRIAN FORMATIONS ROBSON PEAK DISTRICT 329 



section between Robson Peak and Moose Pass, an air line distance 

 of nine and one-half miles (15.2 km.). 



Robson Peak is in a broad, shallow syncline that is more or less 

 broken about its outer limits by faults and minor displacements of 

 the strata. To the northeast and east of the Peak, ridge after ridge 

 exposes the strata that slope in toward the Robson massif and thus 

 present a fine opportunity to study the downward extension of the 

 stratigraphic section from Robson to Moose Pass, where a great 

 fault cuts out the base of the Cambrian series of the region and 

 in the ridges of the Tokana Mountains (pi. 55, fig. i) east and 

 southeast of Moose Pass repeats the Upper and possibly Middle 

 Cambrian beds of Lynx, Phillips (pi. 57, fig. 2), and Titkana Moun- 

 tains east of Robson. 



GEOLOGICAL SECTION 



The oldest Cambrian beds occur on the southwest side of Moose 

 Pass (pi. 55, fig. i). From there the strata are well exposed in Tah 

 Peak, a sharp point (fig. Ii) above the Pass, and then in several 

 ridges to the south on the eastern side of the upper Smoky River 

 valley. The line of the section passes through Tah Peak southwest 

 to Mahto Mountain (pi. 55, fig. 2), and south across Coleman Brook, 

 Hota Clififs, Chetang Cliffs, and Tatay Cliff's (pi. 56, fig. 2), thence 

 south-southeast over Titkana Peak to Phillips and Lynx Mountains 

 (pi. 57, fig. 2) and the ridges to the southeast of Robson Peak. This 

 irregular course of the section is necessary in order to obtain ex- 

 posures of the strata free from snow fields and glaciers, but by fol- 

 lowing the strike of the strongly marked strata it was not difficult to 

 maintain a practically continuous section. 



The time available for actual field work was greatly limited during 

 the season of 1912 by the unusual rainfall. This condition and also 

 the necessity of making a general reconnaissance before determining 

 where to establish the typical section prevented careful measure- 

 ments and the working out of detailed sections. Several horizons 

 were found containing fossils and rather careful estimates made of 

 the thickness of the various formations between Tah Pass and the 

 summit of Robson. 



The oldest rocks noted were quartzite sandstones on the south- 

 west side of Moose Pass and the valley of Moose River below the 

 Pass. The contact of the Lower Cambrian sandstone with the pre- 

 Cambrian rocks was not seen in the Robson District, but to the 

 north, west, south, and southeast of Yellowhead Pass it is finely 



