146 ALASKAN MINERAL RESOURCES IN 1905. 
facts seem to indicate that a subsidence of the land in this neighborhood is going on at the 
present time. 
Along the Arctic shore there is a broad, low tundra with fringing sand spits, behind 
which are shallow lagoons, the largest of which is Lopp Lagoon. Over the flat, or tundra, 
are scattered almost innumerable ponds and lakelets. From the shore the land gradually 
rises to the hills from G to 10 miles back. 
The streams of this watershed are the longest of the region, but their grade is low and 
their course across the Hats is tortuous. 
GECLOGY. 
SEDIMENTARY ROCKS. 
In a general way the rocks run across the York region in broad north-south bands, 
intruded by greenstones, granites, and some more basic rocks. East of a line running 
approximately northeast from the month of Kanauguk River to the Arctic plain the great 
mass of rocks is of limestone, generally thin bedded, which seems to be of Upper Silurian age 
and is known as the Port Clarence limestone. Between York Creek and Mint River is a 
large area of slates, of unknown age, in the south end of which is Brooks Mountain. A 
smaller area of slate lies between California and Don rivers. 
West of the limestone is an area of sedimentary rocks varying from graphitic slate to fine- 
grained false-bedded quart zite. In places, particularly north of Potato Mountain, the rock 
has been jointed into pencil-shaped rhombohedral fragments. Its age is unknown, and 
so far it lia^ not been definitely correlated with t he patches of slate to the east . This slate 
extends from the Kanauguk to a point about 5 miles east of Tin ( 'it v , where it is succeeded 
by a limestone of Carboniferous age, apparently overlying the slate. 
[GNEOl > ROCKS. 
Cape Mountain is a mass of coarse gray porphyritic granite thrust through the limestone, 
and into the latter acidic dikes and sills have been hit ruded in all directions. There are also 
later basic dikes cutting both limestone and granite. The upper 100 to 450 feet of the 
mountain are composed of a dark, line-grained quart z-sericite schist, whose bedding seems 
to be about fiat. Between the schist and the granite is a bed of limestone 10 to 12 feel 
thick. 
On the north of Potato Mountain there are a number of granite dikes with others of a 
somewhat more basic character. 
At Brooks Mountain, Ears Mountain, and Tin Creek are large intrusions of granite, while 
granitic dikes cut across Lost River \ alley at many plates and are also found on King 
River and in the slate area between Don and California rivers. 
Greenstone dikes, probably altered diorites or -till more basic rocks, cut the slates at a 
number of places in the vicinity of York, and basalt or diabase dikes are known on Cape 
Mountain and along Lost River. 
ALLUVIAL DKPOSITS. 
The alluvial deposits are generally shallow. .1 or feet being ordinarily the maximum 
depth of the stream gravels. The depth of the gravels of the Arctic tundra is unknown. 
TIN DEPOSITS. 
LODES. 
LOST EIVER AREA. 
The first discovery of lode tin in Alaska was made in the summer of 1903 on Cassiterite 
Creek, a tributary of Lost River, about 7 miles from the sea, by Me srs. Leslie Crim, Charles 
Randt, and W. J. O'Brien. The place was visited by Arthur J. Collier and the writer 
immediately afterwards, and the occurrence was described by Collier.a A small amount of 
"Collier, A. J., The tin deposits of the York region, Alaska: Bull. U. S. Geol. Survey No. 229, 1904, pp. 
