GENERAL CHARACTER AND CORRELATION 711 



area Pseudornonotis-bearing beds form the upper part of the Triassic sec- 

 tion near Nation River. Eocks belonging at the same horizon occur at 

 many places throughout the Arctic Mountains, being known on Firth, 

 Canning, and Noatak rivers and at Cape Lisburne and Cape Thompson. 



These rocks consist, in general, of shales and flaggy limestones. They 

 contain chert beds in the Chitina Valley, on both shores of Cook Inlet, at 

 Cape Lisburne, at Cape Thompson, and in the Noatak Valley. Volcanic 

 material is present at the head of White River, in the Upper Susitna Val- 

 ley, and on Kenai Peninsula. 



The writer believes that there is an important unconformity at the base 

 of the Pseudornonotis-bearing beds of Alaska and British Columbia. The 

 evidence for this unconformity is as follows : 



In the western part of the Chitina Valley, notably in the valley of 

 Elliot Creek and in the hills between Rock and Copper creeks, shales hav- 

 ing the lithologic and faunal character of those of the McCarthy forma- 

 tion occur not far above the top of the Chitistone limestone, thus appar- 

 ently occupying the normal stratigraphic position of the Nizina limestone, 

 over 1,000 feet thick, which elsewhere separates these two formations. In 

 the vicinity of Skolai Pass, near the head of White River, the Pseudo- 

 monotis zone immediately overlies a Permian ( ?) limestone. There is 

 consequently an hiatus represented in the Nizina Valley, about 20 miles 

 distant, by the Nikolai greenstone, the Chitistone limestone, and the 

 Nizina limestone, which have an aggregate thickness of at least 7,000 or 

 8,000 feet. At Hamilton Bay, Kupreanof Island, in southeastern Alaska, 

 the Pseudomonotis zone is separated from the older Halobia zone (the 

 strata being inverted) by a conglomerate containing fossiliferous boulders 

 of the older limestone. It is evident that the same unconformity is pres- 

 ent on Cumshewa Inlet, Queen Charlotte Islands, where Dawson has de- 

 scribed 47 the relations as follows : 



"On the southeast side of the South Arm flaggy argillites occur. They were 

 observed to become conglomeratic in one place with fragments of the underly- 

 ing [Triassic] limestone, which might be supposed to show that they belong to 

 the coal-bearing [Cretaceous] series. They hold, however, the characteristic 

 Triassic Monotis." 



Further evidence of an unconformity at the base of the Pseudomonotis 

 zone is indicated by the apparent absence at most places of the coral- 

 bearing strata that belong below the Pseudomonotis zone and above the 

 Halobia zone. The fact that in both Alaska and in British Columbia the 



17 George M. Dawson : Report on the Queen Charlotte Islands. Geol. Survey of Can- 

 ada. Report of progress for 1878-1879, p. 82B. 



