DEVONIAN 327 



graptolite faunas at Dease river^ and Kicking Horse pass/" British Co- 

 lumbia, which are referred to the Middle Ordovician by Lapworth. 



DEVONIAN LIMESTONE 



The lowest division of the Devonian is a limestone formation about 325 

 feet in thickness. It is a massive light gray to blue limestone weathering 

 buff and considerably broken by joints. It rests apparently unconform- 

 ably on the graptolite shales described above and is followed in the section 

 by brown shale. The lower 5 feet of this shale may be seen resting 

 directly on the limestone on the bank of the Salmontrout river just above 

 its mouth. The total thickness of this shale is unknown, but, judging 

 from the covered slope extending upward from the limestone along the 

 Salmontrout river, it probably amoi\nts to several hundred feet. Out- 

 crops of the limestone described occur on both banks of the Porcupine 

 immediately above the Salmontrout river, and it is proposed to call this 

 formation the . "Salmontrout limestone," from the Salmontrout river, 

 which is the nearest geographic feature having a name availal^le for a for- 

 mation name. Fossils are abundant throughout this limestone. Its strike 

 and dip are concordant with that of the subjacent Silurian shale and 

 limestone, and afford no evidence of deformation at the close of Silurian 

 sedimentation. 



Although no angular unconformity is shown in the relations of the 

 Silurian and Devonian series where observed, imconformable relations 

 between the two are attested both by the lithology and the faunas. In 

 passing from the Silurian to the Devonian, the lithologic change is an 

 abrupt transition from black shales to very pure limestones. The faunal 

 change is from a Silurian graptolite fauna to a Middle Devonian fauna, 

 the Lower Devonian fauna being absent. The Devonian limestone forms 

 a continuous outcropping cliff 100 to 200 feet high for 1 mile above the 

 Salmontrout river, along the east bank of the Porcupine. It also out- 

 crops on the opposite side of the river in isolated exposures. 



DEVONIAN FAUNA 



The fauna occurring in the Devonian limestone is indicated by the 

 following list : 



* Lapworth : Note on graptolites from Dease river, British Columbia. Canadian Rec- 

 ord of Science, vol. 3, 1888, pp. 141-142 ; Geological Magazine, third dec, vol. 6, 1889, 

 pp. 30-31. 



"Lapworth: Fossils of Kicking Horse pass. Science, vol. 9, 1887, p. 320. 



