198 ALASKAN MINERAL RESOURCES IN 1906. 
been found. On this stream the bed rock is made up of a slabbi 
quartzite, together with schists. Twelvemile Creek has a broad 
flood plain, but nothing is known of the depth of gravels, though 
they do not appear to be deep. Other streams in this part of the! 
Birch Creek basin are said to carry auriferous gravels. A little 
mining has been done on Porcupine Creek, a tributary of Crooked! 
Creek near the mouth of Miller Creek. The valley of the stream is 
wide and the gold in the gravels appears to be much disseminated.' 
The gravels are said to be 12 to 15 feet thick. Some excitement was) 
caused during 1906 by the discovery of gold on Portage Creek, a 
tributary of Medicine Lake, in the southeastern part of the Birch 
Creek basin. Though about $200 worth of gold was said to have been 
taken out of one claim, further prospecting failed to reveal any 
values. 
At various times gold has been reported in the Preacher an| 
Beaver Creek basins, but the presence of values has never been 
established. These basins appear to lie outside of the gold-bearing 
area, though details in regard to the geology are meager. 
CREEKS TRIBUTARY TO YUKON RIVER. 
GENERAL GEOLOGIC FEATURES. 
The influx of prospectors in 1898, following the discovery of the* 
Klondike, led to considerable prospecting along the streams tributary 
to the Yukon between the boundary and Circle. So far as known no 
placers have ever been found in the streams of this region entering trlj 
Yukon from the north. Mission and Seventymile creeks are referreol 
to on page 38, and the present discussion will be confined to Wash.! 
ington, Fourth of July, and Woodchopper creeks, together witll 
some smaller streams. 
So far as known to the writer the gold that occurs on these stream 
is from a different formation than that found in the Birch Creel 
basin, and in at least one place it has its source in a conglomerate 
Therefore the character and extent of the deposits are probabf 
different from those of the placers above described. It must b 
admitted, however, that the evidence at hand is too incomplete t 
permit definite assertion in regard to the bed-rock geology of much c 
this belt. 
The rocks exposed along the Yukon between Eagle and Circle d 
not anywhere include any of the older schists, such as are associate 
with the Birch Creek placers. In fact, over much of this belt tr 
formations are slightly altered limestones, shales, slates, and coi 
glomerates, which do not bear evidence of mineralization and will n< 
attract the placer miner. Locally, however, some of these rocks a] 
mineralized and contain more or less gold. Thus on Nugget Gulc 
