collier.] DISTRIBUTION AND CHARACTER OF THE COAL. 19 
usually of poor quality and of no economic value, are common in these 
tuft's. At a point about 50 miles above Kaltag an attempt has been 
made to exploit them. 
THE COAL. 
GEOGRAPHIC DISTRIBUTION AND CHARACTER. 
Coal of commercial importance is found in two different geologic 
horizons along the Yukon, namely, in the Upper Cretaceous and in the 
Kenai series. The Yukon silts contain some impure lignites, but they 
have no value. It will be shown below that coal seams which have 
been opened up near Nation River may be of Permian age, but these 
appear to be of little future importance. From the standpoint of the 
coal miner, therefore, all of the Yukon coal can be said to be of either 
Cretaceous or Tertiary age. On the map (PI. II) the areal distribu- 
tion of the coal-bearing series along the Yukon is given as far as it 
has been determined, but it has not been found feasible, from the data 
at hand, to differentiate the Cretaceous coals from those of Tertiary 
age. The map also shows the areas of non coal-bearing rocks as far 
as known. These are divided into four classes, the first comprising 
the metamorphosed sediments, the second the Yukon silts, and the 
third the recent alluvium, while the areas occupied by igneous rocks 
comprise a fourth class. The coal prospector should confine his 
search for merchantable coals to the areas occupied by coal-bearing 
rocks. 
It has been noted that the Kenai series occurs in small, isolated areas 
along the Yukon above the mouth of the Tanana. These in some 
cases represent remnants of larger areas, which are now infolded with 
the older beds; in other cases they probably represent separate basins 
of deposition. Outside the region under consideration the Kenai 
series, occurring in small basins, has been found to be one of the most 
widely distributed formations in Alaska. These coal-bearing beds rest 
unconformably on nearly all the older formations that have been 
identified in Alaska, and their conglomerates contain pebbles derived 
from them. The coal beds are not confined to any one definite hori- 
zon in the Kenai. In some instances they are known to be near the 
bottom of the formation; in others they lie near the top. This 
irregularity is what may reasonably be expected, for if the Kenai 
sandstones were deposited in fresh-water basins that were usually not 
connected, the formation of coal beds would probably not occur in all 
the basins at the same time, nor would the coal beds hold the same 
position in the series in all cases. All the coals examined in the Kenai 
basins along the Yukon above Tanana are lignites, or at least are 
lignitic in character. 
The Upper Cretaceous, which is the lower coal-bearing horizon, is 
extensively developed on the lower Yukon. It outcrops along the 
