790 INDEX TO THE STRATIGEAPHY OF NORTH AMERICA. 



P 6-7. MOUNT WBANGBLIi DISTRICT. 



Moffit and Knopf ®°°^ thus refer to the local occurrence in the Mount Wrangell 

 district of deposits which are provisionally assigned to the Tertiary. 



A formation consisting of soft, thin-bedded shales and sandstones, associated with large 



, amounts of well-rounded conglomerate composed mainly of diorite cobbles, occurs in the region 



of Coal Creek, north of White River, near the international boundary. The area in which these 



rocks are exposed is small, but there is some probability that they underlie the volcanic cappings 



of the mesas which form prominent features of this part of the White River region. 



The strata lie nearly horizontal and rest upon older rocks which stand on edge. In places 

 they are hgnitiferous, and petrified wood of exogenous character is common as float in gulches 

 cutting the formation. 



The resemblance of these rocks to those of similar patches scattered throughout the Yukon 

 basin" leaves little doubt as to their Tertiary and probably Kenai age. Rocks of identical 

 character occur near the head of Chitistone River and, like those of the White River region, 

 are covered by a heavy series of volcanic flows. 



P-Q 5-6. FOOTHILLS OF THE ALASKA RANGE. 



The Bonnifield and Kantishna placer districts lie on the northern slopes of the 

 Alaska Range. In course of prospecting for gold, lignites have been located and 

 the field is thus described by Prindle : "^^ 



Deposits containing lignite coal have a wide distribution in the northern foothifls of the 

 Alaska Range, but the only section to be considered here is that extending east from CantweU 

 River to Wood River, a distance of about 50 miles, and northward to the flats. The low spaces 

 within this area between the east-west ridges of old metamorphic rocks are occupied by these 

 deposits. They are for the most part but slightly consolidated and have been so deeply incised 

 by the drainage systems that in places nearly complete sections are exposed. That the present 

 areas are only a part of masses formerly much larger in extent is shown by small isolated patches 

 of these deposits that lie slantingly on the upper slopes of ridges and by weU-worn pebbles 

 derived from them that lie scattered on the tops of the highest ridges, 1,500 to 2,000 feet above 

 the occurrences of the valleys. These deposits have been folded, the flexures being for the 

 most part broadly open, with dips of 30° to 35°, but locally closer, with resultant vertical dips 

 attended in places by consolidation of the gravel beds to conglomerate; in addition, here and 

 there parts of the deposits have been faulted. 



The material comprises' alternating beds of sands, clays, coal, and gravels that are divisible 

 into three parts — an underljdng white deposit composed of angular and some weU-wom, sub- 

 angular, fine quartz gravels, with a large admixture of kaolinic material where the bedrock is 

 feldspathic; an intermediate member of yellowish cross-bedded sands and fine well-worn 

 gravels, dark plastic clays, and coal beds; and an upper member composed almost entirely of 

 gravels. The feldspathic schists produce by weathering a large amount of white clay, and the 

 quartz veins which in places in these rocks are very numerous furnish abundant quartz material, 

 and these characteristics of the old bedrock have gone over into the basal members of the sedi- 

 ments. The transition from the decomposed products of the schists that still retain their 

 structural position to the same materials in the overlying deposits is in some places strikingly 

 exhibited. The thickness of these underlying deposits was not determined, but one section 

 was observed in which 100 feet of them was exposed. The sands and clays of the intermediate 

 member are naturally less conspicuous than the' underlying beds but have in many places 

 become indurated by the burning of the coal beds and baked to a conspicuous red color. The 



"■ Collier, A. J.., Coal resources of the Yukon, Alaska: Bull. U. S. Geol. Survey No. 218, 1903, p. 19. 



