. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology; Zoology. HUNTINGTON" AND GOLDTHWAIT: THE HURRICANE FAULT. 225 hundred feet below the observer, lies black lava that matches the basalt cap on which he stands. He recognizes that in this discordance of altitude of the two parts of the lava sheet he has a measure of the recent fault, which formed the steep scarp. But his eye discovers more than this. Down beneath the lava that lies beyond the cliff he sees the brick-red Kanab sandstone. We can quickly reconstruct the section before him, as it must have looked just
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology; Zoology. HUNTINGTON" AND GOLDTHWAIT: THE HURRICANE FAULT. 225 hundred feet below the observer, lies black lava that matches the basalt cap on which he stands. He recognizes that in this discordance of altitude of the two parts of the lava sheet he has a measure of the recent fault, which formed the steep scarp. But his eye discovers more than this. Down beneath the lava that lies beyond the cliff he sees the brick-red Kanab sandstone. We can quickly reconstruct the section before him, as it must have looked just after the lava flow and just before the recent fault- ing, by imagining the ground on which he stands to sink fourteen hundred feet until the lava cap of the mesa lies alongside the lava west of the fault line. On the east, under the lava, there is lower Moencopie shale ; on the west, under the lava, is Kanab sandstone. The flow of basalt covered an ancient fault. The lava must have flowed across a base levelled fault line where a displacement of about fifteen hundred feet had brought Kanab against Moencopie. The lava itself was then faulted, forming the present Figure 5. The Hurricane fault at Virgin canyon. Near where the canyon of the Virgin river cuts through the Hurricane ledge, there is a condition of things somewhat similar to that just de- scribed (Fig. 5). The steeper part of the escarpment, as before, is the product of the recent fault, which has here a throw of only three hundred feet. Up the canyon, just east of the scarp, a part, at least, of the old fault is shown by an exposure in the canyon wall. Here again the old fault is preserved under a basalt sheet. On the lifted eastern side of the fault, Aubrey limestone lies nearly horizontal; against it on the downthrown side are Moencopie shales that dip steeply towards the west (Plate 3B). On either side of the river, where it crosses the old fault line, warm sulphur springs issue from the foot of the canyon
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Keywords: ., bookauthorha, bookcentury1800, bookdecade1860, booksubjectzoology
