GENERAL GEOLOGY 
2 5 
rite, forming in some places solid compact ore, associated 
with a dark quartzite and with beds of fine-grained mica¬ 
ceous sandstone, greenish feldspathic sandstone and mag¬ 
nesian limestone. Just west of the mine the sandstone is 
cut by a thick diabase dike. 
At the great nunatak of the Columbia Glacier, sand¬ 
stones of the Vancouver Series are traversed by a rhyolite 
dike. It is narrow, disjointed and weathered, but was fol¬ 
lowed by Mr. Palache for more than half a mile. The 
rock, which weathers white, is blue-gray on fresh fracture, 
and shows distinct flow structure parallel to the walls of 
the dike. In thin section it is sparsely porphyritic, with 
embayed or completely rounded quartz crystals and occa¬ 
sional phenocrysts of orthoclase and oligoclase. The 
groundmass is either uniformly and extremely fine-grained 
(179) or beautifully spherulitic (178), the circular spheru- 
lites irregularly disposed, chiefly about the phenocrysts as 
centres of growth, the spaces between them being filled 
with fine granophyric intergrowths of quartz and ortho¬ 
clase. This narrow dike of rhyolite and a single boulder 
of coarse yellowish granite found at the base of the nuna¬ 
tak, were the only rocks of igneous origin noted in the re¬ 
gion about the Columbia Glacier. 
We touched on the east side of Latouche Island, where 
there is also a deposit of copper ore on which work has 
been done. The ore consists of a large body of chalco- 
pyrite and pyrrhotite mixed in places with much pyrite 
and at times with comby quartz. It is said to be an 
impregnation in the black slates of the region. 
The rocks of this series, which have been called the 
Valdes Series by Mr. Schrader, 1 are much more meta¬ 
morphosed than those of the Vancouver Series at Orca. 
They seem to occupy the area between Port Gravina and 
Port Valdes, and to extend far to the northeast on the 
^oth Ann. Rept. U. S. Geol. Survey, Pt. vn, p. 408. 1900. 
