'32 FOKTYMILE, BIRCH CREEK, AND FAIRBANKS PLACERS. Hull. 251. 
able area to the south of the Seventymile; it also crosses Granite 
( 'reck' and the lower part of Hume Creek, and farther west lies to the 
north of the Seventymile. The serpentines, with their diabasic dikes 
and a medium-grained massive gabbro, become prominent in the high 
ridge which extends from the Seventymile toward Charley River. 
Another narrower belt, which also seems to have a northwesterly 
trend, occurs to the south of King Solomon Creek. The rocks are 
found again to the southeast of the Forty mile quadrangle and in 
the far southwest between Chicken Creek and South Fork. The dark 
shales at this locality, which carry gold in calcite seams, are also 
referred provisionally to this formation. These rocks seem to overlie 
unconformably the Forty mile rocks. Their age is probably Devo- 
nian. 
KENAI FORMATION. 
Far younger than the rocks above described are those of the Kenai 
formation of Eocene age. They are best displayed in the lower val- 
ley of the Seventymile, where the river is bounded on either side by 
high ridges of massive conglomerate, with interbedded leaf-bearin 
l fe Xi l ' u b v,J v '^ «■■"•»-"-'-»■*'-' ^""fe 
<» 
shales. These occur on the lower part of Bryant Creek in an almost 
continuous section nearly a mile wide. The creek flows northeast. 
About 4 miles above the mouth occur thin-bedded gray and black 
shales, grits, and a small amount of conglomerate. In the shales are 
numerous heavy, yellow, ferruginous nodules, often containing plant 
remains, which are also abundant in the thin-bedded grits. The strike 
is about N. 70° E., and the dip 15° to the north. About 700 feel 
downstream are precipitous slopes of conglomerate with an east- 
west strike across the stream and a nearly vertical dip. GreaJ 
slabs of this compact rock have fallen from the slopes and lie! 
weathering at their bases. These beds, with possibly some shales! 
occur over a width of about 3,000 feet and are succeeded by 6CJ 
feet of dark and gray paper shales and grit, w T ith the same strike! 
and dip and in close contact with conglomerate on both sides. The! 
shales contain many plant remains, and the sandy beds of the con-j 
glomerate next to them exhibit irregular impressions a foot or more 
long and up to 4 inches wide. These show generally well-definecl 
linear markings, and there seems little doubt that they represent some 
form of vegetable life. The shales are succeeded by 350 feet of coiB 
glomerate, and this by more fine sediments 50 feet thick, composed 
of gray, micaceous, somewhat loosely consolidated, leaf -bearing] 
shales and grits and fine-grained compact shales, where the leaves are 
beautifully preserved. These shale beds, like the others, are in con- 
tact on both sides with conglomerate; that on the downstream side 
outcrops with possibly some interbedded shales for nearly a quarter 
of a mile to a point where a wooded slope descends gradually toward 
