30 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
be taken either as a postulate of this interpretation of the Hurricane 
ledge, or as a consequence following from it: in either case, the expla- 
nation of the plateau topography involves the recognition of two groups 
of rocks, very unlike in their resistance to erosion, so that a period of 
time which only serves for the erosion of a narrow canyon by a strong 
river in the more resistant strata, suffices for the stripping of the less 
resistant strata from great areas by unconcentrated subaerial weathering 
and by the washing of occasional wet-weather streams. 
Tue Secrion NEAR ANTELOPE WasH. — The Hurricane ledge and its 
fault would well repay attentive study along the western border of the 
Uinkaret plateau ; but springs are so few and far between along its 
course that it is difficult of exploration. We rode out to its edge at two 
other points north of the lava-capped spur near Coal spring : one was 
near one of the northwestern volcanoes of the Trumbull area, an isolated 
cone about thirty miles north of the canyon; the other was a mile south 
of the trench cut by Antelope wash. From the first of these points, we 
saw a high lava-capped Permian butte rising over the Shivwits plateau 
about three miles west of the Aubrey strata exposed in Hurricane ledge. 
This seems to confirm the conclusion reached near Coal spring ; for the 
lava-cap suggests that the underlying Permian strata have an approxi- 
mately level surface at an altitude that is far above baselevel to-day, 
but which must have been relatively near baselevel before the lava was 
poured out ; otherwise the Permian surface could hardly have been worn 
so flat as it seems to be. A local complication was here noted at the 
base of the ledge, strongly suggestive of recent faulting, but we had no 
time to descend and study it. 
The view northward showed at a distance of ten or fifteen miles a 
curious offset in the fault whereby a splinter of upper Aubrey at the | 
edge of the Uinkaret bends down and descends southward to the Shiy- 
wits level, as is roughly shown in Figure 9. 
The view from the Hurricane ledge near Antelope was exceptionally 
interesting in its display of brilliant red Triassic clays and sandstones in 
the ten miles of lower land between the base of the ledge and the Vir- 
gin river east of St. George, and in its exhibition of lava-capped Permian 
mesas on the northern terminal slope of the Shivwits plateau. The geo- 
logical wonders of the scene were rivalled only by its exceptional barren- 
ness. Not the least notable feature was the suggestion of extreme heat 
given by the vivid colors of the Trias as well as by the ominous black- 
ness of the lavas. A muddy stream was still running down the channel 
of the wash from the thundershowers of the afternoon before. The dis- 
