68 ALASKAN MINERAL RESOURCES IN 1905. 
STRUCTURAL FEATURES. 
There are two types of structure in this coal field, the line of separation passing through 
the valley of Canyon Creek and agreeing very closely with the division between the anthra- 
cite and bituminous coal. 
The western district , in which the coal is semibituminous or semianthracite, is character- 
ized by open and for the most part fairly regular folds, of which two major and several minor 
synclines occur within the area of coal-bearing rocks. This structure is illustrated in fig. 3.1 
Some faults are present. 
5 
t) ft) 
£ 1-1° 
FIG. 3.— Section from Lake Charlotte to Lake Kwshtaka. 
The eastern district, which lies to the cast of Canyon Creek and Carbon Mountain and ; 
which contains anthracite coal, is characterized by almost uniformly northwestward dips, 
frequently at low angles, and by numerous dikes and sills of igneous rock. The structure ofi 
this end of the field is hardly as simple as the low and apparently uniform dips seem to indi- 
cate. What seems to be monoclinal dip is in reality sometimes close overturned folding in 
which the rocks are bent back on themselves so that the opposite sides of a fold are parallel. 
The rocks are also broken locally by faults, which cause a repetition of the beds; while t here 
are also places where the beds are involved in complex close folding with steep and not oven 
turned dips. 
COAL SEAMS. 
ANTHRACITE. 
The exposures of anthracite at the extreme east end of the area mapped are for the most 
part well up the mountain sides and inaccessible. The following seams were measured and 
sampled: 
Section if miles wpcreek from Fourth Berg Lake, elevation 1,850 feet. 
Dark shale roof. Ft. in.] 
Coal a 8 
Coaly shale 4 
Coal i 11 
Coaly shale 3 
Coal a 8 
Shale floor. 
2 10 
Strike, N. 76° W.; dip, 55° SW. 
Section in gulch at head of Second Berg Lake. 
Sandstone roof. Ft. in. 
Coal, bony 6 
Coal, hard and bright b 2 2 
Sandy shale floor. 
Strike, X. 85° W.; dip, 32° NE. 
About a mile above this, on the north side of the valley and just below the hanging glacier 
a 7-foot bed of anthracite is reported. The sample shown to the writer is very bright, hard 
and not crushed a I all. 
The best exposures of anthracite seen by the writer are in Carbon Mountain, where the 
following sections were measured. 
a Included in sample No. 1, p. 74. b Included in sample No. 2, p. 74. 
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