no2 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
river, all in the glare of burning sunshine except for the deep shadows 
on the south wall of the canyon. | 
At certain points one may see the river for the better part of a mile, 
but the bends in its course soon carry it out of sight. Its most notable 
features are:—an apparently graded flow, the absence of flood-plain 
strips, foam-like patches of whitish sand along the water’s edge, a slope 
of talus for several hundred feet over the river banks, and the projection 
of a delta fan more than half across the channel from the first large 
lateral ravine in the northern esplanade east of the fanlt line. This 
ravine joins the canyon at grade, although its drainage area from an 
amphitheatre in the Aubrey cliffs over the esplanade is not a tenth, 
perhaps not a twentieth of the Toroweap area. The slope of the 
southern wall of the canyon, measured on a photograph, is close to 60° : 
about a quarter of the wall consists of steeply graded, talus-covered 
slopes at an angle of 35° ; the remainder is made up of rock-faced cliffs, 
with slopes of 70° or more. There are five chief cliff belts, the strongest 
of which is on the upper red-wall limestone with a nearly vertical height 
of six hundred feet. 
The salient corner, where the northern esplanade is cut off by the. 
Toroweap fault, affords a superb view of the effects of this dislocation. 
The floor of the southern esplanade is foreshortened in the view 
from a point at its own height ; it is in places bare, in places dotted 
over with cedars like a thinly planted orchard as in Plate 4 B. The 
extension of the esplanade west of the fault on the north side of the 
inner canyon is here concealed by Vulcan’s throne; but it is well shown 
on the south side of the canyon two hundred or three hundred feet 
(according to the topographic map of the district) below its counterpart 
east of the fault. The descent from one level to the other is made 
partly by an abrupt scarp of the esplanade sandstone, and partly by a 
slope of the weaker beds that lie between the esplanade sandstone and 
the red-wall limestone. Directly at the base of the slope lies the sheet 
of lava by which the floor of south Toroweap valley has been held up ; 
the lava west of the fault being just about at the level of the cliff of red- 
wall limestone (under the esplanade sandstone) east of the fault, as is 
clearly shown in Plate 5 A. It was an immense satisfaction to see all this 
from so suggestive a point of view as the corner of the northern 
esplanade. There I spent two memorable morning hours, taking refuge 
beneath overhanging ledges under the corner when the sunshine became 
urpleasantly strong, and then slowly retreating to a larger rock shelter 
near our camp, a mile back, for the hot hours of noonday. 
