730 L. D. BURLING CAMBRO-ORDOVICIAN NEAR MOUNT ROBSON 



(§§ SOc-d, Sla^ o2l)-e) to show that the "new Lower Cambrian snbfanna'^ 

 with Olenellus, referred b}' "Walcott to the "Hota/"^ occurs in the "Tah," 

 nearly 1,750 feet below the base of the Hota, and therefore more than 

 2,250 feet below ATberteUa. Since we have discovered typical Middle 

 Cambrian fossils in the basal layers of the "Hota" or its immediately 

 underlying calcareous beds, we are free to feel a reasonable doubt as to 

 the presence of Olenellus in the "Hota." 



(§ 86.) We have, therefore, no alternative but to draw the line between 

 the Lower and the Middle Cambrian below the "Hota/' Just where to 

 draw it below the "Hota" is, however, a little more difficult (§§ 30/, Zlc, 

 32d-e), for, curiously enough, the immediately underlying clastic series 

 does not yield Olenellus as it does in the Canadian Pacific Eailway sec- 

 tion. Here — that is, in the Mount Eobson region — ^the first beds resem- 

 bling the 20 -foot bed of limestone which has been described^- as forming 

 the top of the Lower Cambrian in the Canadian Pacific section are those 

 of a bed approximately 2,000 feet below the base of the "Hota,^' in the 

 Mumm Peak (north face), section. The highest Lower Cambrian horizon 

 secured by ourselves from the beds underlying the "Hota" is separated 

 from that Middle Cambrian formation by some 1,500 feet of quartzites 

 and arenaceous limestones, and on paleontologic grounds the line between 

 the Lower and the Middle Cambrian merely lies somewhere between. 

 From a stratigraphic standpoint, and in the absence of any evidence of 

 unconformity below, the line appears to be correctly dra^vn at the top of 

 this quartzite series; and, since the top of the Mahto was also drawn at 

 the top of the quartzitic series, the top of the Lower Cambrian and the 

 top of the Mahto coincide. (See §§ 30 and 31.) 



In the Mount Robson region, therefore, an apparently unfossiliferous 

 dominantly quartzitic series approximately 1,500 feet thick separates the 

 highest Olenellus fauna from known Middle Cambrian; and, while we 

 have placed these rocks in the Lower Cambrian, it will be worth while to 

 contrast and compare the section with those in other portions of the 

 Cordillera. 



(§ 8c.) Known Middle Cambrian limestones somewhat abruptly over- 

 lie unfossiliferous quartzites in the Stansbury Range, Simpson Range, 

 Beaver River Range (Cricket Spring), and House Range sections of 

 Utah (first group). In the Onaqui Range, Blacksmith Fork Canyon, 

 East Fork Canyon, Geneva, Wasatch Canyon, and Promontory Point 

 sections (second group), however, there appears to be an almost imper- 

 ceptible gradation between the quartzites and the limestones ; and, since 

 the underlying quartzites in a section (Mill Canyon, Idaho) closely re- 



" Burling: Museum Bull., Geol. Surv. Canada, no. 2, 1914, pp. 106 and 115. 



