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 scarp. 
FicureE 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 walls. 
Within half a mile of the fault, on its downthrown western side, a white 
