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)
There is also a compact, crystalline, gray limestone near the upper
portion of the series, which escaped notice in the cliffs. At the end
of the Pinnacle-pass cliffs, however, where the rocks are turned
northward by the great fault which decides the course of the Seward
glacier, and dip eastward at a high angle, the limestone is well
exposed, and has a thickness of about 50 feet. In many places the
surfaces of the layers are covered with fragments of large _Pecten_
shells. Associated with the limestone there are reddish shales, much
crushed and broken, and a peculiar conglomerate. The pebbles in the
conglomerate are of many varieties, and were observed at places along
the Pinnacle pass cliffs. Their most marked peculiarity lies in the
fact that they have been sheared by a movement in the rocks and
sometimes broken into several fragments which have been reunited,
probably by pressure. These faulted pebbles are characteristic of the
strata from which they were derived. Similar pebbles were afterward
obtained in the Marvine glacier near its junction with the Malaspina
glacier, thus indicating that there are other outcrops of the
conglomerate about Mount Cook, near where the Marvine glacier {171}
has its source. Two quartz pebbles from the conglomerate of Pinnacle
pass are shown in the accompanying illustrations. The larger pebble
(shown in figure 7) is of bluish-gray quartz, and the smaller one
(depicted in figure 8) is of white quartz. The fragments into which
they have been broken are now firmly united. The engravings are
photo-mechanical (Moss process) reproductions from the objects.
[Illustration: FIGURE 7--_Faulted Pebble from Pinnacle Pass_.]
[Illustration: FIGURE 8--_Faulted Pebble from Pinnacle Pass_.]
In the northern and western part of the Samovar hills the rocks of the
Pinnacle system again appear, forming a bold angular ridge, curving
southward and reaching the border of the Agassiz glacier. The southern
face of this range is precipitous and, like the Pinnacle pass cliffs,
exhibits the edges of northward-dipping strata. Its northern and
western slopes are heavily snow-bound. It is in reality a continuation
of the Pinnacle pass fault, but thrown out of line by the cross-fault
which marked out the course of the Seward glacier.
The Yakutat and Pinnacle systems are so easily recognized that their
distribution can be distinguished at a glance, when the outcrops are
not concealed beneath the nearly universal covering of snow. The rocks
of the Yakutat series are heavily bedded sandstones and shales, and
have in general a light-brown tint; while the rocks of the Pinnacle
series are thinly bedded and dark in color, appearing black at a
distance.
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