24 TIN DEPOSITS OF THE YORK REGION, ALASKA. [no. 229. 
The greater part of the York region is occupied by the York Pla- 
teau, which is from 200 to 600 feet above the sea and is a result of 
erosion occurring during the period in which was produced the bench 
described in connection with the Lost River deposits. a 
This plateau is trenched by the streams which drain the region, and 
the valleys have V-shaped cross sections, characteristic of newly estab- 
lished drainage. At the base of Cape Mountain, which rises to an 
elevation of 2,300 feet, the York Plateau has an elevation of about 300 
feet above the sea. The interbedded schists and limestones above 
described form the bed rock of the plateau surface surrounding Cape 
Mountain, but the mountain itself is composed almost entirely of a 
granite boss intrusive in the limestone. The contact relations of the 
granite and limestone have not been studied in detail, but from data 
gathered in the hasty reconnaissances it appears that the granite cuts 
across the bedding of the limestone. This granite has already been 
described under the heading " Igneous rocks." 
The writer's visit to this locality was of necessity a very hasty one, 
and work was hampered by exceedingly rainy weather, so that his 
observations were limited. Specimens of tin ore, however, w T ere 
obtained from surface debris, which undoubtedly came from tin 1 granite 
of the mountain, though the ore was not definitely traced to its posi- 
tion in the solid rock. It is reported that tin ore has been found in 
at least three distinct places on this mountain, and that it occurs in 
somewhat irregular deposits which have an east -west trend. Several 
short tunnels have been driven into the mountain, but are reported 
not to have reached any ore bodies. The granite from some of these 
tunnels is partially altered to greisen and justifies the belief that the 
ore bodies may be not far distant. A sample of this granite, analyzed 
by Mr. Sullivan, of the Survey, was found to contain a few hundredths 
of 1 per cent tin. 
The ore obtained at Cape Mountain differs in general appearance 
from that seen at Lost River. Large pieces of nearly pure cassiterite, 
one of which weighed fully 9 pounds, are said to have been found on 
the surface of the mountain. A specimen which the writer obtained 
weighs approximately 2 pounds and is nearly pure cassiterite, show- 
ing few ciystal faces, but embedded in it and surrounding it are long, 
slender needles of tourmaline. While in this vicinity the writer saw 
a number of large, nearly colorless crystals of cassiterite which were 
practically transparent. Near the end of the season a large amount 
of supposed tin ore was collected on the flanks of Cape Mountain and 
shipped to Seattle, where it was examined by the writer and from it 
samples were selected for study in the laboratory. This supposed ore 
contains very little tin, but several dark crystalline minerals which 
a Collier, A. J., A reconnaissance of the northwestern portion of Seward Peninsula, Alaska: Prof. 
Paper U. S. Geol. Survey No. 2, 1902, pp. 36-39. 
