National Geographic : 1892 May 15
140 C. W. Hayes-Expedition through the Yukon District. glomerate and schist. The district between the Donjek and Koidern rivers is composed almost entirely of white marble and talcose schist, and is the largest observed area of sedimentary rocks between the St Elias mountains and the Yukon. Rocks of Scolai Pass.-As already described, two slightly diver gent ranges, separated by the Chittenah valley, extend toward the west and northwest from mount St Elias. The geology of the northern range is simple. In the walls of Scolai pass, by which the range was crossed, its stratigraphy and structure are magnificently displayed. The rocks are comparatively recent, for the most part Carboniferous, Triassic, and Cretaceous. A bed of limestone about 500 feet thick contains many crinoids and corals, probably of Carboniferous age. Above it are red sandstone and jasper and a great thickness of black shale. Col lections of fossils from the limestone and the black shale were made, but before reaching the coast they unfortunately were lost, with the exception of a single small piece of shale; this, however, contained several tolerably perfect impressions and was submitted to Professor Alpheus Hyatt for identification. He says: " The fossils in the shale are clearly the remains of a Monotis of a Triassic type, allied to M. subcircularis,Gabb, a char acteristic Triassic form in California. This one seems to be distinct specifically, but is evidently of the same age." Interbedded with these sedimentary rocks and penetrating them as dikes are fine-grained, greenish amygdaloid lavas form ing perhaps half of the whole rock-mass. The structure of the range consists essentially of a broad, gentle synclinal, with a highly contorted belt on either side. Excellent examples of typical fan structure were seen in the intensely plicated rocks which form the abrupt northern face of the range. This structure is remarkably well shown in the sides of the gorge from which Kletsan creek issues. The 500 foot stratum of white limestone above referred to is folded in with dark greenish-black eruptive rocks so as to form a double V; the overturned southern synclinal limbs dip southward about 30° and 45°, while the normal northern limbs are nearly hori zontal. This plicated belt on the northern side of the mountains is about six miles wide, and south of it the synclinal in which the beds are practically horizontal (coinciding with the axis of the range) occupies a belt from twenty-five to thirty miles in width.
1893 Feb 08
1892 Mar 31