PINNACLE SYSTEM.
The rocks of this system, as already stated, are best exposed in the great fault-scarp forming the northern wall of Pinnacle pass. They are more varied in composition and have preserved a better record of the conditions under which they were deposited than the sandstones and shales of the Yakutat system.
Only an approximate section of the rocks exposed in the Pinnacle-pass cliff was obtained.
| Sandstone and conglomerate weathering into spires | 500 | feet. |
| Evenly bedded, sandy shale in thin layers | 600 | " |
| Coarse conglomerate; bowlders of crystalline rock | 50 | " |
| Thinly bedded, dark-colored sandstone and shale | 500 | " |
| Reddish conglomerate | 10 | " |
| Light-gray sandstone, with thin, irregular coal seams | 40 | " |
| Total | 1,800 | " |
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 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.
| FIGURE 7—Faulted Pebble from Pinnacle Pass. |
| 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.