GENERAL GEOLOGY 25 



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 



1 20th Ann. Kept. U. S. Geol. Survey, Pt. vn, p. 408. 1900. 



