DISTRAIBURION OF GOLD PD ERO SUS RUN ie NSkeae 
THE deposits hitherto worked on the Yukon River are stream 
avels, and the region in which most work has been done thus 
far lies on the great river and its tributaries near the point at 
which it crosses the eastern boundary of the territory. Along 
the southern coast of Alaska there are several localities at which 
quartz mining is carried on, and some at which placers are in 
operation. A number of deposits exist along the coast in the 
region of Juneau. Of these much the most important and 
famous is the Treadwell mine. The Treadwell, on Douglass 
Island,? produces over half a million a year, from ore which 
averages only $2.50 to $3.00 perton. Thanks to the enormous 
scale of the workings, more than half of the gross yield is net 
profit. The main country rock is a slate of sedimentary origin, 
and probably of Triassic age. It has been penetrated by a 
heavy dike of granite and two other intrusive masses. The last 
of these is a rock of basaltic character, and its eruption seems 
to have accompanied the mineralization. Both the granite and 
the slate were ruptured along a zone which is at some points 
several hundred feet in width, and the interstitial spaces have 
been filled with ore. In the granite the mass was in great part 
reduced to irregular fragments, and these have been decomposed 
and impregnated. In the slate the fractures mostly followed 
the cleavage, and the deposit there assumes the form of what I 
call a “stringer lead.” The claims to the southward of the 
Treadwell are controlled by the same company, and are profit- 
able, but the next claim to the northward is said to be too poor 
to pay. 
Silver Bow Basin lies about three miles north of east from 
‘Note read before the Washington Geological Society, by Mr. George F. Becker. 
2Dr. Gro. M. Dawson wrote a paper on this mine in Amer. Geologist, Aug., 1859. 
960 
