ALASKA COAL FIELDS. 
41 
are consequently not well defined and must be regarded as subject to 
considerable changes by subsequent exploration. They are intended 
to indicate the regions in which new discoveries of coal seem, in the 
light of our present knowledge, to be most probable. The extent of 
the various areas noted above, as well as the area of each individual 
coal field, is shown in the following table, which gives a total of at 
least 1,238 square miles, or 792,320 acres, of known workable coal and 
12,644 square miles, or 8,092,160 acres, of " coal-bearing rocks." 
Areas of Alaska coalfields. 
Known coal 
areas. 
Areas of 
coal-bearing 
rocks, b 
Anthracite: 
Square miles. 
26.4 
4.2 
Square miles. 
30.6 
Semibituminous: 
20.2 
20.3 
14.2 
620 
Matanuska River 
Cape Lisburne 
54.7 
620 
Bituminous: 
Matanuska River 
22 
69 
167 
205 
9 
900 
Alaska Peninsula 
657 
2,490 
1,255 
68 
472 
5,370 
557.3 
5,990 
Lignite: 
Southeastern Alaska : 
10 
304 
16 
50 
Cook Inlet region 
2,565 
300 
20 
216 
52 
83 
1,557 
Bering Sea 
426 
1,736 
681 
6, 654 
Grand total 
1,238 
12,644 
a The differences between the areas given here and those published elsewhere are due chiefly to the 
recognition of four classes of coal instead of three, and the consequent division of the Lisburne areas into 
semibituminous and bituminous and of the Yukon areas into bituminous and lignite, and of similar 
changes in other smaller areas. 
b See explanation on p. 40. 
GEOLOGY OF THE COAL-BEARING ROCKS. 
The geologic position of Alaska coals is distributed through hori- 
zons in the Carboniferous, the Jurassic, the Cretaceous, and the Ter- 
tiary. The abundance of the coal and the extent of the areas increase 
progressively from the older to the younger horizons, reaching their 
culmination not later than the Miocene. 
It should be noted in this connection that the old belief that the 
age of coal is an index of its quality does not hold uniformly in Alaska 
or elsewhere. This belief contains a partial truth in Alaska as in other 
regions, but other factors are always locally of greater weight. The 
