duttos ] GRAND CANON AT THE TOROWEAP. 117 



diversified. The chasm is seen through the entire stretch it) the Uin- 

 karet Plateau and reaching a few miles into the Sheavwits. But about 

 twenty miles westward it makes a southward turn and disappears. 

 From the north the Toroweap Valley descends from near Mount Trum- 

 bull. It is cut down only to the base of the upper canon wall and 

 opens into the main chasm on the level of the plain above the inner 

 gorge. There is reason to believe that at some prior epoch it was cut 

 a few hundred feet deeper than its present floor, and was subsequently 

 built up by many floods of basalt coming from the cones on the Uinkarct 

 and by considerable quantities of alluvium washed from its cliffs and 

 overlooking mesas. On the south side of the Grand Canon is a valley 

 quite the counterpart of the Toroweap. It enters the main chasm directly 

 opposite to the Toroweap, so that the two form the arms of a transept, 

 the main chasm being regarded as the nave. Vulcan's Throne is situ 

 ated almost exactly at the intersection of the axes of nave and transept. 



It would be difficult to find anywhere else in the world a spot yield- 

 ing so much subject-matter for the contemplation of the geologist: 

 certainly there is none situated in the midst of such dramatic and 

 inspiring surroundings. The chasm itself, with its marvelous story of 

 erosion, and the two lateral valleys adding their quotas of information 

 are grand subjects indeed; but other themes are disclosed which arc 

 scarcely less surprising and suggestive. The cone stands immediately 

 upon the line of a large fault. And never was a fault and its conse- 

 quences more clearly displayed. The Toroweap fault is one of six 

 which at wide intervals traverse the Grand Canon district from north 

 to south with a rude approximation to parallelism. It is the smallest 

 of the six. Twenty miles north of the chasm no trace of it is visible. Its 

 beginning there is small, but as it approaches the chasm it increases in 

 the amount of displacement; and at the crossing of the river the shear 

 or "throw" is between 000 and 700 feet. In the wall-face of the inner 

 gorge it is disclosed as clearly as a draughtsman could delineate it on 

 paper. The masses of horizontal limestones and sandstones, displaying 

 their fretted edges and lines of bedding, advance from the eastward in 

 the face of the wall until they reach the vertical fault plane. Then 

 they "break joints" and drop at once six or seven hundred feet, and 

 continue westward as before, but at a lower level. The whole topog- 

 raphy goes with it. Looking beyond to the upper Avail of the outer 

 chasm the "jog" where the break occurs is plainly seen. The whole 

 platform of the country .is dropped to the westward. The plain between 

 the upper palisades descends by a single step from east to west across 

 the fault by an amount equal to the displacement, and the inner gorge 

 and the whole chasm becomes by so much reduced in depth. 



Excepting the dislocation itself, the faulting does not appear to have 

 been accompanied by any injury to the strata. Not a trace of shat- 

 tering, crumbling, or mashing of the beds is discernible. All looks as 

 clean and sharp as if it had been cut with a thin saw and the smooth 



