14: TIN DEPOSITS OF THE YORK REGION, ALASKA. [no. 229. 
arenaceous, and sometimes calcareous character, and are of very line 
texture. They are much jointed and broken by lines of cleavage into 
rhombohedral blocks and pencil-shaped fragments. The bedding is 
often obscured and sometimes obliterated by the highly developed 
joint structures. The age of these slates has not been determined. In 
1900 they were correlated by Brooks a with the so-called Kuzitrin 
slates, which outcrop along the northern base of the Kigluaik Moun- 
tains. The work of the writer in 1901 pointed to the conclusion that 
they are older than the Port Clarence limestone, but this fact has 
not yet been definitely established. There is some indication of 
faulting along the contact of this slate belt and the limestones to the 
southeast. 
West of the slates there is a narrow belt of highly altered limestone 
or marble more or less interbedded with micaceous schists. This belt, 
about 4 miles in width, lies between the slates on the east and a large 
mass of granite on the west, the latter forming the peak known as 
Cape Mountain. Some obscure fossils collected during the past season 
indicate that these limestones are either of Devonian or Carboniferous 
age. The stratigraphic relations of this limestone to the slates on the 
east have not been definitely determined. 
SURFICIAL DEPOSITS. 
The unconsolidated gravels and silts form the youngest group of 
sediments of the region. On the sketch map these deposits are shown 
mantling an area bordering the Arctic coast. This is the western end 
of a very extensive gravel deposit which covers the low Arctic coastal 
plain of Seward Peninsula from Cape Espenberg to Cape Prince of 
Wales. 6 These deposits extend to the base of the hills and in the 
valleys merge with the stream gravels with which they probably have 
common origin. In the southern part of the York region these snr- 
ficial deposits are confined to the creek beds and narrow strips along 
the coast, and are usually too small to be shown on the map. All of 
these gravels are water-laid deposits, there being no evidence of glacia- 
tion. They form a part of the great Quaternary mantle that is so 
extensively developed in Seward Peninsula and adjacent portions of 
Alaska. The gravels, which are of economic interest because they 
locally contain concentrations of stream tin, will be described in 
another part of this paper. 
a Brooks, A. H., Richardson, G. B., and Collier, A. J., A reconnaissance of the Cape Nome and 
adjacent gold fields of Seward Peninsula, Alaska, in 1900: Special report on Alaska, U. S. Geol. Survey 
1901, p. 133. 
& Collier, A. J., Reconnaissance of the northwestern portion of Seward Peninsula, Alaska: Prof. 
Paper U. S. Geol. Survey No. 2, 1902, p. 25. 
