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Show WESTEEK POETION OF THE AQUAEIUS. 295 Water Pocket fold on the east appears to have been, during the latter part of the Cretaceous age, an island. It is apparently possible to designate roughly the positions of large portions of its east and west coast-lines. In a word, those coast-lines may have been approximately coincident with the axes of those two flexures. The northern part of this island cannot at present be ascertained, because the lavas have deeply buried it, and there is not even sufficient basis for conjecture. But of the portions now indicated it is possible to infer that the length of this island must have been at least 90 miles and its maximum width about 35 miles. The northwestern angle of the Aquarius is laid open by an immense gorge. Amass of lavas and conglomerate more than 2,000 feet thick is revealed, and beneath them lies the Tertiary. Near the opening of this gorge the Grass Valley fault cuts across it, throwing down the platform to the west. Along the western base of the Aquarius the faulting becomes very complicated, and the displacements are great in their vertical extent. The faults are repetitive, or " stepped," with numerous instances of the dropping of large blocks between faults of opposite throw. These blocks usually sag in the middle, and there is occasionally some chaos produced in the component masses. An effort was made to find the proper restoration, but I am doubtful whether it has been very accurately done. (See stereogram.) The western wall of the Aquarius, which looks down upon the southern portion of Grass Valley and the Panquitch Hayfield, is of great grandeur, rising more than 4,000 feet above the valley below. Apparently it is composed of volcanic materials from top to bottom, but the thickness of the volcanic masses is less than it seems at first. The wall rises by successive steps, and each step represents a fault, so that the aggregate thickness of lava and conglomerate probably will not exceed 2,000 feet on the average. The rocks are mainly trachytic, but a large proportion of augitic andesites is associated with them. At the summit of the plateau near the western crest and upon the thrown blocks which are successively passed as we descend, are numerous fields of ancient basalt much eroded, and presenting a similar appearance to the scattered basalts spoken of in the preceding chapter as occurring upon the surface of the Awapa. Their |
