696 G. C. MARTIN TRIASSIC ROCKS OF ALASKA 



the highest known Triassic rocks of California and Nevada. This fossil 

 is very closely related to, if not identical with, Pseudomonotis ochotica 

 Keyserling, which is characteristic of the boreal fades of the Noric of 

 Europe and Asia. 



Nutzotin Mountains and Alaska Range. — A well defined, although 

 probably discontinuous, belt of Triassic rocks extends through the south- 

 ern foothills of the Nutzotin and Alaska Eanges from near the Canadian 

 boundary to the headwaters of Susitna Eiver. The eastern part of this 

 belt, which is known as the Nabesna-White Eiver district, lies north of 

 the Chitina Valley and is separated from it by the Wrangell Mountains, 

 in which the Quaternary and late Tertiary lavas and the existing glaciers 

 conceal the underlying Mesozoic strata. Because of this lack of con- 

 tinuity and because of differences in the character of the sediments, the 

 rocks in the two districts are somewhat difficult of correlation. 



The Triassic rocks in the vicinity of Skolai Pass 12 include shales and 

 overlying lavas, tuffs, breccias, etcetera. These rocks rest on a Permian ? 

 (Artinskian) limestone. The shales are about 300 feet thick and contain 

 interbedded tuffs in their upper part. The overlying pyroclastic rocks 

 are of undetermined thickness. Both the shales and the overlying vol- 

 canic beds contain Pseudomonotis sub circular is (Gabb), and the latter 

 have yielded also an undetermined species of Clionites (Shastites) . The 

 presence of Pseudomonotis subcircularis indicates that these rocks are to 

 be assigned to the same general position as the McCarthy formation of 

 the Chitina Valley, although that formation, as now known, does not 

 contain volcanic material. 



Limestones and shales of Upper Triassic age have been found in the 

 vicinity of Cooper Pass, 13 which is in the southern foothills of the^Nut- 

 zotin Mountains, about 50 miles northwest of Skolai Pass. The Triassic 

 limestone occurs in close geographic and structural association with a 

 massive Permian (?) limestone, but the stratigraphic relations to the 

 Permian (?) limestone are not known. The fauna of the Triassic lime- 

 stones and shales of Cooper Pass, as now known, includes only Pseudo- 

 monotis subcircularis (Gabb). The presence of this species, together with 

 the similarity of the beds to the thin-bedded limestones and shales at the 

 base of the McCarthy formation, suggests a correlation with rocks at that 

 horizon. 



12 C. W. Hayes : An expedition through the Yukon district. Nat. Geog. Mag., vol. 4, 

 1892, p. 140. 



F. H. Moffit and Adolph Knopf : Mineral resources of the Nabesna-White River dis- 

 trict, Alaska. U. S. Geol. Survey Bull., No. 417, 1910, p. 17. 



18 F. H. Moffit and Adolph Knopf : Mineral resources of the Nabesua-White River dis- 

 trict, Alaska. U. S. Geol. Survey. Bull., No. 417, 1910, pp. 27-32. 



