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Show 180 GEOLOGY OF THE HIGH PLATEAUS. degradation, and the altitudes of the eruptive centers increased. Now and then came a long interval of repose, indicated by the quiet accumulation of considerable, though very local, masses of stratified conglomerate here and there. Again the energy was renewed and fresh outbreaks occurred, followed by a long rest. After a protracted series of alternating eruptions and unequal intervals of rest there came a very long period of repose to be reckoned by a geological standard of time, during which these massive conglomerates accumulated and the huge volcanic piles were razeed-â€"a period in which there may have been eruptions, but in which, on the whole, the ceaseless erosion leveled down the highlands and leveled up the lowlands. But the building of the conglomerate beds did not close the volcanic cycle. After they had acquired their enormous bulk there came another period of outbreaks, some of them in the old localities, others in new ones, pouring fresh sheets over the wasted centers and over their scattered and stratified debris, piling up fresh mountains of lava and generating a new topography. This second series of eruptions differed strikingly in litho-logical character from the first. The earliest series in the Tushar, so far as known, is andesitic and trachytic ; the second is rhyolitic and basaltic. In the northern part of the range the dominant rock of the second series is rhyolite, with a limited occurrence of basalt. In the southern part of the range the relative abundance of the two groups is reversed, rhyolite being uncommon, and in most areas being replaced by true trachyte. These beds cover both the central part of the Tushar and the conglomerates at the southern end. They lie upon the eroded surface, filling old ravines and spread out in broad sheets over the tabular summit, obliterating upon the surface the definition between the conglomerate and the degraded mass which furnished its materials, though the junction is exposed in the eastern front of the range by the great fault which at a later epoch was formed by the general uplifting of the whole mass. The southern termination of the Tushar is marked by a group of lofty summits a few hundred feet lower than Belknap at the northern end and Delano near the center, but full 1,600 feet higher than the wall and tabular summit which connects them with the central part of the table. They are |