424 , J. BARRELL RECOGNITION OF ANCIENT DELTA DEPOSITS 



Banded slates of the Orange groiip, by D. D. Cairnes.^^ — These red 

 and green banded slates or metamorphosed mud stones are included in a 

 group of sediments provisionally named tlie Orange group, which is at 

 least 6,000 feet in thickness and occurs extensively along that portion of 

 the 141st meridian (the Alaska-Yukon international boundary) between 

 latitudes 66° 00 and 67° 00, which was geologically studied and mapped 

 by the writer^^ during the past season (1911). Terranes that probably 

 coiTespond to, and that at least closely resemble this group both litho- 

 logically and stratigraphically, also occur on the Upper Macmillan and 

 Upper Stewart rivers and have been briefly described by both McConnell 

 and Keele.^° Triassic fossils were found by Keele in slates underlying 

 the banded mudstones in the Upper Stewart Eiver region; and a con- 

 siderable number of imperfect invertebrate remains were collected by 

 the writer along the 141st meridian from the lowest beds of the Orange 

 group, and these remains have been identified by Dr. T. W. Stanton as 

 being of Mesozoic and in his opinion probably of Cretaceous age. 



On account of the somewhat highly altered character of these Orange 

 beds and the general scarcity of their outcrops, no complete section of 

 the group has been obtained at any one point, and the lithological char- 

 acters of the members composing it vary considerably throughout the 

 areas in which they have been identified. At one point banded slates 

 200 to 250 feet in thickness occur, occupying a central position in the 

 Orange group; these pass downward into dark gray to black slates and 

 phyllites and are overlain by greenish gray sandy shales. ^Approximately 

 25 miles farther north, however, the banded slates are at least 1,800 feet 

 in thickness; there they directly overlie Silurian limestones and dolo- 

 mites and are in turn overlain by black slates. In no place was any 

 gradation noted from the red and green banded mudstones to other beds, 

 the change being invariably abrupt. 



The color bands range from those that are scarcely perceptible to 

 others several feet in thickness, and in places either the red or the green 

 persists for 50 to 100 feet or even more to the complete exclusion of the 

 other color. In general, however, the bands are from one-fourth to 2 

 inches in thickness, and throughout several hundred feet of beds the 



1** By permission of the Director of tlie Geol. Surv. Branch, Dept. of Mines, Canada. 



18 D. D. Cairnes : Summary Rept. Geol. Surv., Dept. of Mines, Canada, 1911 (in 

 preparation). 



20 R. G. McConnell: "The Macmillan River, Yukon district." Ann. Rept. Geol, Surv. 

 of Canada, vol. xv, pp. 31A-84A. 



.T. Keele : "The Upper Stewart River region. Yukon." Ann. Rept. Geol. Surv. of 

 Canada, vol. xvi. pp. l.'?C-18C. 



J. Keele: "A reconnaissance across Mackenzie Mountains on tlu^ Telly. Ross, and 

 Gravel rivers, Yukon and Northwest territories." Geol. Surv., Dept. of Mines, Canada, 

 No. 1097, 1910, pp. 33-3G, 39-40. 



