YUKON PLACER FIELDS. 113 
The coal-bearing beds outcrop for about 15 miles along the river and were traced about 1 miles to 
the east. The area of this coal field can be safely estimated at 60 square miles at least, and may be 
many times that. The beds are seldom exposed except along the river and stream valleys, for else 
where they are usually deeply buried under Pleistocene gravels. 
What promise to be workable coal beds were found at two localities during the hasty reconnaissance 
on which these notes are based. The most important of these are on Healy Fork, an easterly tribu- 
tary of Cantwell River, which it joins from the east about 40 miles from the Tanana. The coal beds 
are well exposed in precipitous bluffs along the north valley wall of this site;, in. * * * While the 
beds are largely made up of sandstone, yet the layers lying immediately adjacent, to the coal are most 
often clay and sandy shales. One bluff about 2 miles from the Cantwell was examined in some detail. 
In this section 200 feet of sandstone and conglomerates formed the basement member and rested uncon- 
formably on the phyllites of the metamorphic series. This bed was overlain by about 250 feet of soft 
sandstone, shales, and coal. In the entire section the coal aggregated about 125 feet in thickness, 
contained in about 15 seams. Of this 125 feet probably 60 feet were of a fairly good grade of lignite. 
The largest seams were 20 feet in total thickness, but included considerable bone and shale. In char- 
acter the coal varied from a fibrous, impure lignite, which is entirely worthless, to lignites which may 
have commercial value. The lignite of better grade is of a lustrous black color, and has a conchoidal 
fracture. The seams were accessible only along the outcrop, where they were made up of noncoherent 
lignite. A sample taken almost at random from one of the larger si ams was analyzed by Dr. E. T. 
Allen, of the United States Geological Survey, with the following result: 
Analysis of coal from Healy Fork of Cantwell River. 
Moisture 13. 02 
Volatile matter 48. 81 
Fixed carbon 32. 40 
Ash .-,.77 
100. 00 
This analysis shows that the coal is a fairly good Kgnite. In considering it, it should be borne in 
mind that the short time given to the study of the locality makes it quite possible that seams of 
better grade were overlooked. 
The second locality where lignites were found is on Lignite Creek, so called, a few miles north of 
Healy Fork. At this place the croppings show fewer seams, and these are of less thickness. These 
lignites, as far as determined, were of no higher grade than those of Healy Fork. North of Lignite 
Creek, and apparently higher hi the series, seams of fibrous, impure lignites and carbonaceous shales 
are not uncommonly interbedded with the sandstones. It is not likely that any of these have any 
prospective commercial value. In the opinion of the writer the best coals in the basin are near the 
base of the sandstone series. 
Topographically these coal seams are exceptionally well located for mining. Though they have 
been known since 1898, the isolation of the locality has precluded any possibility of their development. 
Should a railway ever be built through Caribou Pass from Cook Inlet, as has been proposed, it is quite 
possible that this coal field might receive development. 
GEOLO(;V. 
BED ROCK. 
The country rock or bad rock throughout most of the area between Chatanika and Little 
Chena rivers is quartzite-schist and quartz-mica-schist, generally in thin alternating hods. 
in places feldspathic and very commonly containing garnets. Graphitic schists are common 
and there is some fairly massive crystalline limestone and some greenstone schists in places 
very garnetiferous. The schists have been closely folded and strike northeast and south- 
west. The main structural planes vary from nearly horizontal to nearly vertical. The 
alternating layers of the blocky quartzite-schist and the very micaceous quartz-mica-schist, 
which decompose readily, give rise to a bed-rock surface of varying influence on the dis- 
tribution of the gold. With a blocky bed rock gold sinks along the structural planes to a 
distance sometimes of several feet, while the compact, clayey mass of the softer beds offers 
an impervious layer which gold can not penetrate. 
Intrusive biotite and hornblende granites occur in parts of the area, notably in the ridge 
south of Gilmore Creek, on Twin Creek, a tributary of Pedro Creek, in Pedro Dome, and at 
the head of Chatham Creek. Some of these occurrences are porphyritic rocks with feldspar 
crystals an inch or more in diameter, while others are fine and even grained. All of these 
