NO. 4 PRE-DEVONIAN SEDIMENTATION 1 63 



The develo])ment of a narrow trough at the close of Middle Cam- 

 brian time within the area of the northern extension of the Bow 

 Trough is mentioned in the description of the Sawback Trough. 



A comparison of the three sections is given in figure i6, p. 156. 



Longitudinal undulation. — The extent of a longitudinal undula- 

 tion, or a tipping of the bottom, of the Bow Trough during the deposi- 

 tion of the Lower and Middle Cambrian formations is shown by the 

 thinning out of the Middle Cambrian Eldon formation from a thick- 

 ness of 2,728 feet (831.5 m.) at Mt. Stephen (P on map) to zero 

 in the section on the Saskatchewan River about 50 miles (80.5 km.) 

 to the north (D on map). The subjacent Stephen formation per- 

 sists ; also the superjacent Arctomys formation which is conformable 

 with the Stephen (see fig. 22, p. 168). The Arctomys is nearly five 

 times as thick in the Glacier Lake section (B on map, pi. 25) as at 

 Mt. Bosworth (R on map). 



GOODSIR TROUGH 

 Plate 25 and fig. 14 



West of the Bow Trough and east of the Beaverfoot Trough 

 {K, pi. 25) and subparallel to it a deep narrow trough was developed 

 and gradually silted up in Upper Cambrian time by fine, argillaceous 

 and siliceous muds that ultimately formed the laminated Chancellor 

 shales 4,500 feet (1,371.6 m.) thick; calcareous-siliceous sediments 

 that formed the Ottertail limestones 1,825 feet (556.3 m.) thick and 

 the Goodsir shales and limestones 6,400 feet (1.950.7 m.) thick, a 

 total of over 12,700 feet (3,870.9 m.) of Upper Cambrian and possi- 

 bly some later sediments, and there may have been earlier Cambrian 

 deposits of which there is no known record. 



In the absence of fossils from the upper 5,500 feet (1.676.4 m.) 

 of strata of the Goodsir formation we are unable to determine the 

 age of that part of the section. I have searched in vain on the flanks 

 of Mt. Goodsir for traces of fossils in the abundant talus from the 

 Goodsir formation above the lower fossiliferous 500 feet (152.4 m.) 

 and Dr. Allan met with no better success. These limestones and shales 

 are even more barren of indications of life than the 4,500 feet 

 (1,371.6 m.) of Chancellor shales which have an occasional faint 

 outline of a fragment of an Agnostus or the cranidium of a small 

 trilobite. None of the above mentioned formations has been recog- 

 nized either east or west of the area assigned to formations of the 

 Goodsir Trough, and they do not appear to have been deposited in 

 the trough for a greater distance than 120 miles (193.1 km.) and a 



