544 INDEX TO THE STEATIGEAPHY OF NORTH AMERICA. 



color, which is indicative of considerable carbonaceous material in its composition. In texture 

 it is fine grained throughout. * * * 



Studies of the Carboniferous and Triassic strata of the Wrangell district hare not been suflS.- 

 ciently detailed to afford evidence as to where the line between these two formations should be 

 drawn. Above the massive basal series of limestones there is a series of thin-bedded limestones 

 with shaly partings, which is apparently in perfect conformity with the underlying beds and 

 which passes by gradation into the black shales above. These black shales contain the fossils 

 by means of which the Triassic age of the formation has been determined. The provisional 

 and arbitrary line between the two formations has been placed at the top of the massive lime- 

 stone series. The thickness Of the Chitistone formation, as thus defined, is somewhat variable. 

 Its maximum development is probably in the region of Nizina River, where it reaches a thickness 

 of approximately 2,000 feet. In the Kotsina and Strelna region its thickness is somewhat less, 

 but it can not be made out that there is any progressive thinning toward the west. * * * 



The rocks which have been included in the Triassic series comprise all the strata that lie 

 above the Chitistone limestone and below the unconformable Kennicott formation, of Jura- 

 Cretaceous age. In the lower part, and resting conformably upon the Chitistone limestone, is 

 a series of thin-bedded limestones, in strata from a few inches to a foot or more in thickness, 

 supported [separated ^ by thin partings of black shale. The thickness of this member is approxi- 

 mately 1,000 feet, and the Hmestone, so far as observed, did not contain fossil remains. Above 

 the thin-bedded limestones, and sharply defined from them, are black shales containing occa- 

 sional bands of impure limestone, locally affording fossils, from which the age of the formation 

 has been determined. The thickness of the upper member of the Triassic is very great, possibly 

 more than 3,000 feet, but no opportunity was offered for its direct measurement, since its occur- 

 rence as the surface formation beneath strata lying unconformably upon it, together with the 

 attitude which it has assumed as the result of folding and faulting, renders its relations compli- 

 cated and obscure. A few thin flows of greenstone, similar to that of the Nikolai series, were 

 observed here and there interbedded with the black shales of the Triassic. The Triassic series 

 may be easily recognized from its general homogeneous nature and the fine-grained character 

 of its black carbonaceous shales. 



Locally the thin-bedded limestones are very intricately folded and contorted. 



P 8. STEWART BIVEB SECTION, YUKON PROVINCE. 



Keele *^*^ assigns to the Triassic certain rocks in the northern Rocky Mountain 

 section, where the map of North America shows undifferentiated metamorphic 

 Paleozoic. He says: 



The crystalline limestone, provisionally classed as Upper Paleozoic, rests unconformably 

 on the crystalline schists, while it is apparently overlain by Triassic rocks. No fossils were 

 found and the contact with the Devonian rocks to the north was not seen. A similar rock 

 mass occurs on the MacmiUan River which was classed as Carboniferous from evidence of some 

 fossil remains found in that locality. 



This occurrence also overlies crystalline schists unconformably and is followed by what 

 are probably Mesozoic rocks. 



The rocks grouped as Triassic are almost altogether of sedimentary origin. Thin bedding 

 and diversity in the color and composition of the beds are characteristic features. They have 

 been greatly folded and crumpled in some localities, while in other places they are horizontal. 

 Cleavage planes have been developed and certain of the beds have undergone slight alteration 

 during the processes of mountain building. 



The rocks which underlie the eastern extremity of the area marked Triassic on the accom- 

 panying map sheet are chiefly made up of sandstones, grits, red slates, limestone, and some 

 volcanics, while toward the western end shaly argillites with thin quartzite and limestone beds 

 prevail. Beds similar to the latter also occur in the section to the west. 



