172 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 75 



same type in the Beaverfoot, Glacier. Lake, and Sawback Troughs, 

 but the Glenogle graptolite fauna of the Reaverfoot Trough has not 

 been found in the Glacier Lake Trough, although there is a strong 

 probability that it may be present in the region west of Mons Peak 

 in the area of the upper Bush River drainage basin. 



We know little of the Glacier Lake Trough northwest of Glacier 

 Lake, except that it extended 24 miles (38.6 km.) as far as Wilcox 

 Pass at the head of the North Saskatchewan River, and had 

 open communication to Robson Peak District more than 96 miles 

 (154.5 km.) northwest of Wilcox Pass. 



ROBSON TROUGir 



The typical section of this trough in the Robson District is 174 

 miles (279.9 kill-) north-northwest of the liow N'alley, where the 

 great formations of the Bow Trough are so finely exposed to view, 

 and 120 miles (193.1 km.) north-northwest of the section of the 

 Glacier Lake Trough. It is now bounded on the southwest by Protero- 

 zoic Beltian sandstones and shales of the ridges of Little Grizzly and 

 Whitehorn Peaks of the Selwyn Range, and on the northeast by the 

 great Moose Pass fault between the Lower and Upper Cambrian 

 formations that extends from Moose Pass south-southeast down the 

 canyon of Moose River and north-northwest towards and into the 

 high broken ridge northeast of the Smoky River Canyon. At Moose 

 Pass the Lower Cambrian is thrust over the Upper Cambrian lime- 

 stones, and from their character I am inclined to think that these 

 L'pper Cambrian and presumably later formations were deposited in 

 a trough that began to form in early Upper Cambrian time east of 

 the Robson Trough after deposition of sediments in the Robson 

 Trough seaway had ceased. 



The Robson Trough as now interpreted, after being narrowed by 

 compression and faulting, has a width of 14 miles (22.5 km.) on a 

 line extending from Moose Pass southwest to Little Grizzly Peak 

 above Lake Kinney. If the Upper Cambrian and other pre-Devonian 

 formations north-northeast of Moose River were included in the 

 Robson Trough and not in a trough adjoining it on the northeast, 

 the width of the Robson Trough as now outlined would be corre- 

 spondingly increased to 22 miles (35.4 km.) or perhaps 24 miles 

 (38.6 km.). 



The known Paleozoic deposits of the Robson Trough have a thick- 

 ness of 13,300 feet (4,053.8 nL ) exclusive of any that may have been 

 deposited east of the ^loose Pass fault. These include Ordovician ?, 



