GEOLOGY. 
17 
STRATIGRAPHIC SU( CESSION. 
The variety of the rocks and the close folding which they have undergone have 
rendered difficult the attainment of definite knowledge regarding their sequence, 
thickness, and contact relations. Their areal distribution, so far as observed in the 
narrow belt of the country traversed, is shown on the accompanying geologic map 
(PI. I), and the provisional order of stratigraphic succession is outlined in the fol- 
lowing tabular statement: 
Provisional tabular statement of stratigraphy. 
Age. 
Formation name. 
Contact relation. ' Lithologic character. 
Recent 
Stream gravels. 
Bench gravels. 
Conglomerates, sandstones, and con- 
solidated clays. 
Pleistocene 
Unconformity to 
Paleozoics. 
Pennsylvania!! or Per- 
mo-Carboniferous. 
slates. 
Gray, greenish, and black shales with 
thin siliceous beds. 
Gray and blue, partly siliceous lime- 
stones, greenstones, quartzites, and 
slates. 
Conglomerates and fine fragmentals, 
slates, and interbedded limestones. 
Cherts, slates, and greenstones. 
Rampart and pos- 
sibly other for- 
mations. 
(Fortymile and 
Birch Creek.) 
Unconformity 
Quartz-mica and garnetif erous schists. 
Quartzite schists. 
The oldest rocks are believed to be the schists, predominantly quartzite-schists, 
which occur southeast of the White Mountains in the ridge which forms the western 
limit of Chatanika Valley, and the garnetiferous quartz-mica-schists with associated 
highly crystalline limestones which occupy a small area in the Rampart region 
along Minook Creek in the vicinity of Ruby Creek. Their age is unknown, and 
they are referred in this report to the pre-Devonian. The rocks from the White 
Mountains westward, inclusive of the Rampart region, are mostly of Paleozoic age, 
and the evidence of the few fossils collected indicates the presence of both Devonian 
and Carboniferous rocks. There is a possibility that some of them are Silurian, but 
in the absence of positive criteria for their further separation only two divisions 
have been made. Those regarded as Devonian include a variety of rocks differing 
greatly in lithologic character and occurring throughout most of the area. Cherts, 
slates with interbedded coarser fragmentals, greenstones, limestones, and quartzites 
are the most characteristic types. 'Along the northern edge of the hill country and 
at one locality south of Hess Creek fossils determined as Carboniferous were 
obtained, but the extent and contact relations of the Carboniferous rocks have not 
yet been determined. The rocks provisionally classed as Cretaceous are of doubtful 
age. They occur on Wolverine and Lynx mountains. On Wolverine Mountain 
fragmentary fossils were found which indicate an age not older than the Lower 
Cretaceous. The Kenai rocks occur along the Yukon and to a short distance up the 
valley of the Minook. High gravels, regarded as Pleistocene, are found locally 
along the larger streams to heights of 400 to 500 feet above them. The present 
valleys are occupied by stream gravels covered generally with muck and moss, and 
the thickness of the entire deposit, so far as developed on the gold-producing creeks, 
rarely exceeds 20 feet, but exceptionally is of much greater depth. 
Bull. 280—06 2 
