HUNTINGTON AND GOLDTHWAIT: THE HURRICANE FAULT. 231 
the foothills of the Pine Valley mountains, on the east it was limited by 
the upstanding Carboniferous limestone of the Bellevue ridge, over 
which as a rule it could not flow. In certain places, however, the lime 
stone pitches down so as to pass below the level occupied by the pene- 
plain of that time. Wherever this is the case, the basalt spread out to 
the eastward and covered the bevelled edges of the softer strata that 
overlie the Carboniferous. The most marked example of this is two or 
three miles south of Dry canyon at an elevation of sixty-three hundred 
feet just east of the Hurricane fault (Fig. 7). Here the level surface on 
which lies the uplifted lava is composed of Moencopie shale, Shinarump 
conglomerate, Painted Desert shale and sandstone, and Kanab sandstone, 
all dipping strongly to the east. Where the same strata are exposed to 
erosion the hard Shinarump and Kanab form strong cuesta-like ridges 
Figure 7. 
Bellevue ridge four miles south of Dry canyon. 
separated by valleys excavated in the soft Moencopie and Painted 
Desert (Fig. 3). Only under conditions approaching closely to base- 
levelling would it be possible for a level surface such as that beneath 
the lava to truncate smoothly strata of such varying hardness. 
(3) Portions or THE ANCIENT SURFACE NOT CovEeRED BY Lava. 
At the mouth of the Virgin canyon, as we have seen, lava seems to 
have flowed across the fault line from the downthrown side and to have 
been soon checked by an escarpment of limestone rising nearly four 
hundred feet. A reference to the illustration (Plate 3 B) shows in the 
middle of the picture a precipitous slope, the scarp of the modern Hurri- 
cane fault. This rises three or four hundred feet to a terrace a few 
hundred feet wide formed by the uplifted eastern portion of one of the 
lava flows. Behind this the ascent consists of rounded maturely dis- 
sected slopes of quite a different character from the youthful cliffs below 
