216 ALASKAN MINERAL RESOURCES TN 1906. 
was reported to be two sluice heads. The bed rock is principally 
quart zitic schist, with some associated carbonaceous schist and green 
stones. Small basaltic dikes were observed in a few places cut lino; 
the schists. Throughout most of the valley the stream gravels are 
composed of material derived from the bed rock, but in the lower pari 
of the creek these rather fine subangular schist gravels become mixed 
with material derived from the heavy Moose Creek wash that rests on 
a bench over 150 feet vertically above Eureka Creek. In the process 
of downward cutting through which the drainage system has passed 
these bench gravels, comprising bowlders of granodiorite, greenstone, 
hard conglomerate containing chert pebbles, and metamorphic slates, 
all of these being materials mostly unlike those characteristic of the 
Eureka Valley, but entirely similar to those of the Alaska Range, have 
become intimately mingled with the local deposits. 
Mining has been confined for the most part to 2 miles of the valley 
immediately above the mouth. The thickness of the deposits that 
are being worked ranges from 1 to 5 feet and the width is in most 
places that of the stream gravels, which is rarely more than 100 feet 
and in some places less than '20 feet. The gold is mostly on bed rock 
or within it to depths of 1 to -\ feet, but all the gravel from surface to 
bed rock is generally shoveled into the boxes. The richest ground 
was in the first half mile above the mouth, where many nuggets were 
found, the two largesl o[' which were worth $186 and $678. Nuggets 
were not confined to this pari of the creek, however, and some worth 
as high as $40 have been found 2 miles above the mouth. The nug- 
get v gold is generally of a lighter color than the finer grade. The gol< 
found in the upper part of the \ alley i.s mostly rough and gritty. Aver 
age assay values were reported ranging from $15 to $16 per ounce 
The proportion of black -and accompanying the gold is small. Herd 
and there pieces of stibnite occur in the gravels, and these have been 
derived, probably, like similar occurrences on Caribou ('reek, from 
veins in the schists. The association in this respect is similar to that 
of the Fairbanks region. 
The reason for the richness of the gravels near the mouth has often 
been a subject of inquiry and it might be supposed that a part of the 
gold at least was derived from the heav}^ Moose Creek bench gravels 
through which Eureka ('reek has cut. So far as could be learned, 
however, these bench gravels are not known to carry payable values, 
and the explanation is rather to be found in the riffle efficiency of large 
bowlders in retaining gold that would otherwise be carried out from 
the smaller valley along with the finer wash. A decrease of grade of 
the smaller stream near the mouth may also be a factor. 
All the gravels are worked by the open-cut method. Boxes are 
given grades ranging from 7 to 9 inches per box. There is but little 
