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Show MOUNT MARVINEâ€"MORAINE VALLEY. 269 under the northeast corner of the Fish Lake Plateau. They are Lower Eocene, equivalent to the Bitter Creek of Powell. The altitude of the ridge forming Mount Terrill declines towards the south until a lofty col or "saddle" is reached, which divides it from Mount Marvine. The latter is one of the most striking features of the region. It is a long ridge reduced to a mere knife-edge at the summit, and having rocky fronts on either side, sloping about 60°. A transverse section of the upper 2,000 feet of the mountain would be an equilateral triangle. For several years it was named by our parties The Blade. When seen from the south or north it has a most abrupt and peaked appearance, which becomes more pronounced the nearer we approach it. Viewed laterally from Summit Valley at its base, it presents a serrated summit, notched with many gaps and bristling with many cusps. The altitude of the mountain above the valley is about 2,700 feet and 11,400 feet above the sea. ' It consists of alternating trachytes and augitic rocks, resting upon Lower Eocene strata. The thickness of the volcanic beds is, in tbe aggregate, from 1 ,^00 to 1,800 feet, being least at the northern end, and increasing towards the south. There is a succession of beds having the same general lithological characters as those in Fish Lake Plateau, except that the augitic members seem to be less numerous but more massive. Here, also, the dominant rock is the argilloid variety of trachyte. The origin of this mountain becomes quite apparent when studied from both sides. It has been isolated, like a gigantic butte, from the adjoining country by the erosion of the valleys upon either flank. The inception of this work is very ancient, since it undoubtedly antedates the uplifting of the platform on which the mountain stands, and may therefore be referred to any epoch more ancient than the latter part of the Pliocene and more recent than the Eocene. MOUNT HILGARD AND MORAINE VALLEY. Before proceeding southward it is desirable to look briefly at Mount Hilgard and at the intervales which separate it from Mounts Terrill and Marvine. From Summit Valley we may easily cross the col which separates the two latter summits, and descending the other side we find ourselves in |