74- FORTYMILE, RIRCH CREEK, AND FAIRBANKS PLACERS, [bull. 2Blj 
party during the summer of L904 on streams which showed no evi- 
dences of having been prospected or even staked, and the held for 
the prospector to the east of the Fairbanks region is still a large one. 
The study of the older camps emphasizes another important fact 
which must be borne in mind, and that is that even in a small area 
where the geologic conditions are apparently the same, the occur- 
rence of gold in sufficient quantity to pay for working may be limited 
to but a few creeks, and while there is always the possibility of find- 
ing workable deposits in the schists of the Yukon-Tanana region, 
there is no reason for expecting a uniform distribution of such 
deposits. 
On the trail to Rampart the schists were not observed after leaving 
the ridge which extends along the northwest side of Chatanika River. 
The country to the northwest is geologically and topographically of 
a different character and more closely related to the Rampart region 
than to that already described. The change is indicated by the 
jagged limestone ridge known as the " White Mountains," which 
extends in a northeast-southwest direction about 15 miles northwest 
of Chatanika River. 
ECONOMIC DEVELOPMENT. 
The present valleys have been formed by the physical and chemical 
work of the streams aided by the weathering of the rocks. Most 
of the resultant waste material has long since been removed, but 
mantling the bed rock of the valleys are unconsolidated deposits com- 
posed of rock fragments, of materials derived from rock decomposi- 
tion and of resistant minerals originally disseminated in small quan- 
tities through the rocks. These deposits, accumulated and arranged 
largely through the agency of water, roughly represent the concen- 
trates from large masses of country rock and within themselves have 
undergone a further concentration, until the heavier constituents lie 
on the bed rock or even within it to a depth of several feet along 
the cracks and crevices. The presence of considerable gold in 
these deposits has made them of much economic interest and a 
knowledge of their character, arrangement, and distribution becomes 
important with reference to' the extraction of the gold. 
There are several characters common to the stream deposits of all 
the creeks; the grade of the bed rock on which they lie is gradual; 
the grade of their surface is about 100 feet to the mile; they are 
mostly deep and in most localities frozen throughout the year; a 
section shows generally a layer of muck underlain by barren, and byj 
gold-bearing, gravels; the gravels are composed of about the same 
kinds of rock, have undergone about the same amount of wear, are oi 
the same degree of coarseness, and are similarly arranged. The 
thickness of the different layers varies widely and the maximum 
