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Show MOUNT TEEEILL AND MOUNT MAEVINE. 267 truth, it seems little doubtful that the Fish Lake Plateau is a great conter of eruption. A general fact in support of this view is that in three directionsâ€"north, south, and eastâ€"and in all intermediate directions, the mass of erupted material attenuates gradually. Whether this be true also of the west side it is impossible to say, because the great monocline carries everything down beneath the alluvium of Grass Valley. But in the other directions we can form a fair notion of the general arrangement of the total extravasation, and the attenuation and radiation from a central locality is sufficiently clear. The most probable view of the original arrangement is that the lavas emanated from many orifices and fissures scattered over the surface of an extensive volcanic pile, not unlike that of Mauna Loa, but on a smaller scale. From the outlet of Fish Lake, at its northeastern end, we may pursue our way down the noble valley which carries the effluent stream. About 4 miles from the outlet we again enter Summit Valley, and, turning northward, we may ascend it to the first camping-ground from which we started to ascend the plateau. On the trail thither we pass two great terminal moraines projecting from the openings of gorges cut back into the plateau mass. Like the one projecting into the lake, they are well preserved and quite typical in their features. MOUNT TEEEILL AND MOUNT MAEVINE. Upon the eastern side of Summit Valley rise two conspicuous masses, which present to the eye nothing suggestive of a plateau. The northern one is Mount Terrill, the southern is Mount Marvine, both being in the prolongation of the same axis. Although in external form they are great mountain piles, their origin is due to circunidenudation, just as a great butte owes its individuality to the removal of the strata around it. They consist of lavas, resting upon Lower Tertiary calcareous beds, and both the lavas and the sediments are nearly horizontal so far as stratification is concerned ; but the lavas were obviously outpoured over a much eroded surface, with hills and valleys of some magnitude. The volcanic sheets may have been continuous with those of Fish Lake Plateau., since they have the same lithological characters and varieties as the more striking trachytic |