NON METALLIFEROUS MINERALS, SOUTHEASTERN ALASKA. 79 
GYPSUM. 
OCCURRENCE. 
Within the last two years extensive developments have been made 
m beds of gypsum at Iyoukeen Cove, on the east side of Chichagof 
"sland, with encouraging results. The extent of this deposit, which 
)ccurs in the bottom of a valley, is practically unknown. There are 
>nly two exposures of this rock on Gypsum Creek, namely, at the 
ower and upper mine workings 1 mile from its mouth, and the entire 
irea except a few outcrops of a cherty limestone is deeply buried by 
t dense undergrowth. The gypsum beds apparently overlie the Car- 
>oniferous rocks exposed along the southwestern shore of the cove 
ind forming the southwestern valley divide, though the area of con- 
tact was buried under deep gravel deposits along the beach and in 
lie valley. They are temporarily assigned to late Carboniferous or 
Permian formations. To the north the mountain is made up of a 
granite mass intruding the older limestone beds. 
The geology in the immediate vicinity of the gypsum beds is ob- 
jure and neither foot nor hanging wall has been exposed in the mine 
workings. Bluffs of a cherty limestone striking northwest and dip- 
)ing to the northeast are exposed near the entrance to the tunnel 
it the lower workings. The gypsum beds in the tunnel and lower 
evels have an east-west to N. 70° E. strike, with a northerly dip of 
50° to 60°. Channels representing old watercourses and now filled 
vith gravel wash are numerous throughout this deposit. These 
'ravels resemble unconsolidated conglomerate beds and have been 
nistaken for both hanging and foot wall of the gypsum beds at points 
n the workings. A careful inspection of the gravels shows that the 
vash has the same character as that now in the creek bed. Of 
significance is the presence of granite cobbles corresponding to the 
ntrusive mass at the head of the creek, which invaded the area sub- 
sequent to the deposition of the gypsum beds. Dikes of a basaltic 
■ock were present in the beds, and one of these occurring at the south 
>nd of a drift on the first level was mistaken for the foot wall of the 
leposit. 
DEVELOPMENTS. 
This deposit, the property of the Pacific Coast Gypsum Company, 
)f Tacoma, Wash., was extensively developed during last year. A 
vharf 2,000 feet in length extending to deep water, with rock bins 
)f 1,000 tons capacity, has been built, and a railroad to the mine work- 
ngs a mile from the shore completed. Rock bins of 1,500 tons 
capacity and a shaft house have been erected at the mine. At the 
ower workings a shaft 190 feet deep has been sunk, and from this two 
evels consisting of 600 feet of drifting have been extended, exposing 
