An Expedition to Mount St. Elias, AlaskaRussell, Israel C. (Cook)
History
An Expedition to Mount St. Elias, Alaska
Russell, Israel C. (Cook)
Alaska -- Description and travel; Saint Elias, Mount (Alaska and Yukon)
Although the rocks of this system are stratified, it is impossible to
determine their thickness, for the reason that they have been greatly
crushed and overthrust. This is well illustrated in the Hitchcock
range, which, as already explained, trends about northeast and
southwest, and is composed of strata of shale and sandstone, having a
nearly east-and-west strike and a uniform dip toward the northeast.
Were the rocks in normal position their thickness would be incredible.
In addition to this negative evidence, there is the crushed condition
of the strata to show that movement has taken place all through their
mass; and in a few instances thrust faults were distinguished, dipping
northeastward at about the same angle as the lines of bedding. In the
crushing to which the rocks have been subjected the shales have
suffered more than the sandstones, and have been drawn out into
wedge-shaped masses, the sharp edges of which usually point toward the
northeast, which is presumably the direction from which the crushing
force acted.
The hypothesis that the rocks in the St. Elias region have been
crushed and overthrust explains many otherwise {169} inharmonious
facts, and accounts for the superposition of the St. Elias schist upon
rocks of the Yakutat system.
Coal has been discovered in the rocks of the Yakutat system about two
miles west of the southern end of Disenchantment bay, and is reported
to be of workable thickness. I saw thin lignite seams at the surface
at this locality, but as the shafts were filled with water I was
unable to examine the coal in the openings, and cannot vouch for its
thickness. Samples obtained from the mine show it to be a black
lignite which would apparently be of value for fuel. Fossil leaves are
reported to occur in connection with the lignite, but these have never
been seen by any one who could identify them.
The rocks of the Yakutat system, wherever seen, dip northeastward,
except when greatly disturbed near fault-lines. East of Disenchantment
bay the inclination of the beds is from 15° to 20°; farther westward
the dip increases gradually all the way to the Hitchcock range, where
the prevailing inclination is from 30° to 40°, and frequently still
greater. Beneath Mount Malaspina and Mount St. Elias the Yakutat
sandstones dip northeastward at an angle of about 15°, and in the
hills west of Icy bay the dip is about the same. Exceptions to the
prevailing dips occur along the immediate shore of Yakutat bay,
northwest of Knight island, and at the southern extremity of each of
the mountain spurs between Yakutat bay and Blossom island. At these
localities the rocks are frequently vertical or nearly so, owing their
high dip to the proximity of lines of displacement. The faults
indicated by these unusual dips also mark the boundary between the
mountains and the seaward-stretching plateau of alluvium and ice.
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