26 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
The view westward down the canyon, Plate 5 B (see also Dutton, b, 
Atlas sheet V. upper view) is very unlike the eastward view. The nor- 
mal esplanade of the southern Uinkaret, enclosed by Aubrey cliffs, is 
seen south of the canyon; it is eleft by a ravine that is fed with wet- 
weather wash from an Aubrey amphitheatre of moderate dimensions, 
very much smaller than the south Toroweap ; yet this ravine descends 
rapidly and joins the river in the canyon bottom at grade. In this 
respect, it resembles the ravine in the northern esplanade east of the 
fault, already described. The lava-covered esplanade of the Uinkaret is 
seen north of the canyon: its enclosing Aubrey cliffs are almost com- 
pletely hidden under the huge floods of lava that sweep down from a 
throng of vents on the plateau, and the floor of the esplanade is banked 
up to form an inclined plane. The lava cascades follow re-entrants of the 
esplanade border into the canyon, but are not distinctly traced all 
the way to the river. The cascades have a slope of 20° or 30°, while 
the upper half of the southern canyon wall has an average slope of 40° 
or 45°. The difference may be due to the abrasive or melting action of 
the lavas as they poured over the rim of the esplanade. The general 
effect of these unequal slopes is to give the canyon here an unsymmetrical 
cross-section. It is possible that the asymmetry may have been increased: 
by the action of the lavas in pushing the river against its southern bank, 
and thus making it undercut the southern wall more actively than the 
northern ; for the lower part (1500 or 2000 feet) of the wall has a slope - 
of 65° on the south and rather under 60° on the north. The river 
itself is seen for a long mile of apparently placid flow: it is here as 
further east bordered by talus rather than by bare rock ; patches of 
whitish sand lie on the banks here and there, and a few fan-deltas 
project from side ravines a third or a half way across the river. Be- 
yond the terminal corners of the north and south esplanade of the 
Uinkaret block in the middle distance, there are glimpses of the Shiv- 
wits plateau, dropped a thousand feet from the corresponding upland 
surface of the Uinkaret. The view is closed by a long mesa surmounting 
the Shivwits, apparently a lava-capped mass of Permian beds. 
The Hurricane Fault. 
Previous Statements. — The Hurricane fault is, according to Dutton, 
like the Toroweap fault of modern date, younger than the beginning of 
the canyon cycle: the evidence for this conclusion being the relatively 
small retreat of the great cliffs of Aubrey limestone known as the 
