114 ALASKAN MINERAL RESOURCES IN 1905. 
are comparatively fresh and have been intruded in the schists since the metamorphism of 
the latter. Acidic granite intrusives so common in the Fortymile region have not been 
observed. Recent fresh olivine-basalt, probably extrusive, is occasionally found. 
Quartz veins are common in the schists, sometimes attaining a thickness of 2 or more 
feet, but are not so abundant that the quartz becomes a conspicuous constituent of the 
gravels. Stibnite has been found in places on Chatham Creek as a vein a foot or more 
thick in the schist, parallel, so far as could be learned, with the structure of the latter. 
Float of the same material at the head of Cleary and Esther creeks indicates further occur- 
rences of this mineral. There has been much search for gold-bearing quartz in the ridge 
between Cleary and Pedro creeks, and a considerable area of mineralized rock to the south- 
west of Pedro Dome has been found that is reported to carry values. 
ALLUVIAL DEPOSITS. 
The constant weathering of the rocks produces loose material of varying coarseness 
which covers the fresher surface beneath until removed. Outcrops of bed rock in the Fair- 
banks region are confined mostly to the summits of the ridges and to the steeper slopes of 
the valleys, while on the gentler slopes and in the bottoms of the valleys the bed-rock sur- 
face is covered with a mantle of material ranging from a few feet to over 100 feet in thick- 
ness. This mantle is composed partly of heterogeneous talus which is continually working 
down the sides of the valleys and partly of the material in the valley floors which has ben 
worked over so many times by running water that it has a fairly uniform structure through- 
out. All of these deposits are. for the most part, frozen throughout the year. 
As the streams generally flow close to one side of their valleys these deposits are mostly 
on one side. Their upper surface slopes gradually toward the base of the hills. The bed 
rock surface, so far as known, is in general nearly flat oral least lias a very gentle grade hill- 
ward from the creek. The deposits are in most cases separable into three divisions, which, 
from surface to bed rock, are referred to by the miners as muck, barren gravels, and pay 
gravel. 
The muck varies in thickness from a few feet to a maximum of about 70 (vvt, the line of 
separation between it and the underlying gravels being fairly sharp. It is a black deposit. 
containing a large amount of material derived from the decomposition of moss and other 
vegetation, with a considerable percentage of clay and sand, either intermingled with the 
organic material or as layers and thin lenses distributed irregularly through the mass. 
Horizontal beds of ice several feet in thickness are sometimes present. 
The underlying gravels, ranging in thickness from 10 to over 00 feet, are derived from the 
rock occurring within the areas drained by each particular stream. As quartzite schist is 
the most common bed rock and also the most resistant to the process of wear, the largest 
proportion of the coarse material in the gravels is composed ol it. The gravels also include' 
quartz-mica and graphitic schist, some vein quartz, and some igneous material, mostly 
granite. An occasional mammoth tooth and bones of other- animals now extinct are also 
found. The coarse material, being mostly quartz-schist, occurs as more or less flattened 
angular pieces but slightly waterworn. Few of them exceed a foot in diameter and the 
proportion of bowlders is therefore small. The line material is composed partly of smaller 
pieces of the more resistant rocks and partly of clay, derived from the decomposition of the 
micaceous and graphitic schists. There is also a small percentage of individual minerals 
released by the process of weathering. Though the proportion of clay in the barren gravels 
is small, in the pay streak it is large. All the material, both coarse and fine, is irregularly 
intermingled, the larger pieces being usually nearly horizontal. The deposits in general arc 
such as would be formed by an overloaded stream. 
The pay gravels resemble those above them, but contain ;i considerable amount of clay 
which adheres tightly to the gravel and to the surface of the blocky fragments of bed rock. 
This clay is prevailingly of a yellowish color in the more shallow diggings and of a bluish 
color in the deeper gravels. The proportion varies, but there is in most cases sufficient 
present to render the pay gravels easily distinguishable in the drifts from the barren ground 
