NO. 4 PRE-DEVONIAN SEDIMENTATION l6l 



ceous muds which now form the Mt. Whyte hmestones and shales 

 as they occur at the base of Castle Mountain in the Bow Valley, at 

 Mt. Assiniboine and Mt. Bosworth on the Continental Divide, and 

 their western outcrop at Mt. Stephen. The trough, now 20 to 30 miles 

 (32.2 to 48.3 km.) or more in width, continued to deepen during the 

 time of the deposition of the limestone of the Middle Cambrian 

 Cathedral formation. 1.2 12 feet (3'"*9.4 m.) ; the Stephen. 640 feet 

 (195. 1 m.) ; and the Eldon. 2,728 feet (831.5 m.) ; a total of 4,580 

 feet (1,395.9 ^^-^ o^ limestones before a shallowing of the seaway 

 resulted in the deposition of the Arctomys siliceous silts that marked 

 the close of Middle Cambrian time and the beginning of the deposition 

 of the Upper Cambrian formations. After the de])osition of the 

 Arctomys silts and fine sands. 268 feet (81.7 m. ) thick.^ the seaway 

 again deepened and the deposits now forming the L^pper Cambrian 

 limestones of the Bosworth formation 1,587 feet (483.7 m.). the 

 Paget and Sherbrook 1,735 ^^^^ (528.8 m.) were laid down, a total 

 thickness,with the Lower and Middle Cambrian sandstones and lime- 

 stones, of 10,170 feet (3,099.8 m.). As far as we now know, the 

 Chancellor shales of the Goodsir Trough do not follow the Sherbrook 

 limestones and they were not deposited within the Bow Trough. 



About the time sedimentation in the Bow Trough ceased, or just 

 before, calcareous sediments were being deposited in the then forming 

 Goodsir Trough in an area now occupied in part by the Van Horn 

 Range. These calcareous deposits were later buried beneath a great 

 thickness of argillaceous and siliceous muds that now form the Chan- 

 cellor shales. The latter may have been deposited and subsequently 

 removed by erosion from part of the area east of their present surface 

 outcrop, but my impression is that when the floor of the Bow Trough 

 was elevated and the long period of limestone forming deposits ab- 

 ruptly ceased with the close of the Sherbrook, it was only within the 

 limits of the Goodsir Trough that the fine argillaceous and siliceous 

 material, now forming the Chancellor shales, was deposited in the 

 Goodsir seaway. The limestones beneath the base of the Chancellor 

 formation in the Van Horn Range are probably of Upper Cambrian 

 age, but until diagnostic fossils are found, it will not be practicable 

 to correlate them with any of the known formations of the Bow 

 Trough. 



Near the eastern side of the Bow Trough at Ghost River (/ on 

 map), about 500 feet (152.4 m.) of late Lower Cambrian sand- 



*At Glacier Lake the Arctomys formation has a thickness of 1,386 feet 

 (422.5 m.). 



