60 RECONNAISSANCE IN NORTHERN ALASKA IN 1901. 



sedimentary origin, is more micaceous, and contains much less quartz and more 

 greenstone-schist, of igneous origin. In some localities, however, it very much 

 resembles the more altered phases of the schists to the east of the Koyukuk. in the 

 Slate Creek diggings, which also have been correlated with the Lake quartz-schist of 

 Chandlar River. That the Totsen series extending beneath the younger formations 

 in the Koyukuk Valley may connect with the Slate Creek schists is not improbable, 

 especially since the Bergman series, which occupies a large part of the intervening 

 Koyukuk Valley, seems to rest unconformably upon both, 



STUVER SERIES" (PRE-DEYONIAN) . 



Character and occurrence. — The next of the older groups of rocks to be consid- 

 ered is the Stuver series, comprising the oldest rocks exposed in the northern portion 

 of the Endicott Range, and apparently forming the core of the north axis. (See 

 section on PI. III.) The rocks of this series are principally conglomerates, with 

 interbedded layers of quartzite, which toward the top pass into slate and shale. 

 The pebbles composing the conglomerate are practically all siliceous and consist 

 of black, slate-colored, red, green, and bluish flint and milky-white quartz. They 

 range in size from less than an inch in diameter to cobbles, and in a few instances 

 approach bowlderets. The cement is siliceous, usually dense, and often contains 

 grains of cryptocrystalline or aphanitic silica, undoubtedly derived from the same 

 parent rock as the pebbles. Great force is required to break the rock with the 

 hammer, and, when broken, the fracture plane is almost invariably found to take a 

 direct course, traversing any pebbles, though perfectly sound, that may lie in its path: 

 in fact, the cementation is so firm as to form of the conglomerate, as a whole, a rock 

 substantially as hard as the hardest flint pebbles that are included in it. 



The various colors of the pebbles in the conglomerate make it a very conspicuous 

 rock, so that it is easity recognized where its fragments occur in Pleistocene and 

 intervening formations. These fragments are conspicuous in the Lower Carbonifer- 

 ous rocks succeeding the Lisburne series, and are also represented in the Lower and 

 Upper Cretaceous and in the Tertiary formations. No one of the parent rocks from 

 which the various types of flint pebbles of the Stuver series have been derived has 

 yet been observed. The specimens found in the placer mining gulches to the 

 northeast, on the west side of the Koyukuk, and referred to by the prospectors as 

 "emerald" and "adamant," probably represent flint pebbles derived from the Stuver 

 conglomerate. 



The interbedded quartzites in the Stuver series are medium grained and excep- 

 tionally hard and siliceous, and are usually of a gray or sometimes a pinkish or red- 

 dish color, while the slate is dark. 



aThe name applied to this series is taken from Mount Stuver, situated east of the Anaktuvuk, and named for a 

 member of the party. 



