CIRCLE PRECINCT. 199 
i tributary of Washington Creek, slates of Cretaceous age are found 
vhich are permeated with quartz veins, some of which must yield 
yold, as the associated alluvium is auriferous. The writer was not 
ible to study this locality, but it appears that the coarse gold occurs 
n small patches on the bed rock. This occurrence, though probably 
)f small commercial import, has a far-reaching significance, as it 
ndicates that there has been an intrusion of mineralized veins since 
)hese younger rocks were deposited. The writer is, however, of the 
>pinion that this mineralization is not general enough to encourage 
he search for placers where these Cretaceous slates form the country 
•ock. 
The occurrence of gold in the conglomerate has an entirely different 
significance. There appears to be a fairly well defined belt of con- 
glomerate running parallel to the Yukon from Seventymile Creek to 
3irch Creek, near the big bend. Both in the Seventymile basin and 
>n Woodchopper Creek placers have been found which must have 
lerived their gold from this rock. Therefore the conglomerate 
nust, in part at least, be auriferous. 
This conglomerate was probably laid down in Tertiary time, after 
he mineralization of the older rocks, and its gold content is com- 
Darable to that of the present placers. Such auriferous conglomer- 
ites have long been known in the Yukon region, having first been 
10 ted by Spurr, a who termed them " fossil placers." There is no 
evidence that the conglomerate itself carries sufficient value to pay 
'or milling, though this is not impossible. The fact that the asso- 
ciated placers are only of moderate richness argues against any con- 
siderable values being found in the parent rock. 
Much of the conglomerate is only loosely consolidated and weathers 
so readily that it is easily mistaken for high bench gravel. As a result 
prospectors sometimes assume that it marks an old river channel and 
pxpect to find very rich leads. Though it is not impossible that the 
conglomerate represents the deposit of an old watercourse, it by no 
means follows that such a deposit would be any richer than the 
placers of the present stream. The term "old channel" has a very 
alluring sound to those who are familiar with the occurrence of gold 
in California. Even if this conglomerate should locally be found rich 
in gold, only such parts of it as are decomposed could be mined by 
placer methods. Therefore the gold in it, except where it has served 
jto enrich present streams, has now no commercial significance. 
The double concentration which must have taken place while the 
gold of these placers passed from its original source in the bed rock 
through the conglomerate and into the alluvium of the present 
streams is favorable to the formation of rich placers, yet none have 
o Spurr, J. E., Geology of the Yukon gold belt, Alaska: Eighteenth Ann. Rept. U. S. Geol. Survey, 
pt. 3, 1898, pp. 365-366. 
