. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology; Zoology. 20 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. has no fellow on the west side of the gulch where the slope consists wholly of tuff. Some of the tuff stands up in little ridges bordering the base of the ash cone and seems to have a steep dip to the west. The vertical displacement here indicated by the lava bed may be one hundred feet or more. A northward continuation of this subrecent movement is suggested by a low west-facing lava scarp that may be traced for a mile or more north of Vulcan's throne on the easte
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology; Zoology. 20 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. has no fellow on the west side of the gulch where the slope consists wholly of tuff. Some of the tuff stands up in little ridges bordering the base of the ash cone and seems to have a steep dip to the west. The vertical displacement here indicated by the lava bed may be one hundred feet or more. A northward continuation of this subrecent movement is suggested by a low west-facing lava scarp that may be traced for a mile or more north of Vulcan's throne on the eastern side of Toroweap valley floor. A still more recent movement is indicated by a small but distinct scarp, about twenty feet in height, that traverses a gravel wash on the east side of the south Toroweap valley, somewhat east of the main fault line. This scarp was seen in a sunset view from Vulcan's throne, when in spite of its distance of about three miles, the low western sunshine LSPLANADL. ESPLANADE- .'_' / j f REIDWALL 1 M. Figure 7. Sketch section at Vulcan's Throne. brought it distinctly to sight. A significant amount of faulting must therefore be recognized as having occurred near the canyon at least, after the esplanade had been formed and after lavas had been poured on its floor. On the other hand, there seems to be no sufficient reason for regarding the chief movement on the Toroweap fault, amounting to six hundred or seven hundred feet according to Dutton, as having occurred in the canyon cycle. Analogy with the neighboring great faults would suggest an earlier origin in the plateau cycle ; this opinion is not at all contradicted by the dislocation of the esplanade, and it is suppoi'ted by the considerable width attained by the Toroweap valleys, north and south of the canyon, as explained in my earlier article (b, p. 143, 184). The decrease of the displacement northward along the valley reported by Dutton (b, p. 93) is probably more apparent than real; the heavy lav
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