96 
THE GRAND CASON DISTRICT. 
about 1,600 feet below the summit; another protrudes about 1,200 feet be- 
low, and still another about 600 below the crest. A fourtli dike ap])a- 
I'ently leads directly to the vent of the cone and no doubt constituted the 
pipe of the volcano. Now a brief scrutiny shows very conclusively that 
these dikes were made when the lateral goi’ge and main chasm had much 
less depth than that which they have now attained. It is manifestly impos- 
sible that a dike of basalt could rise hundreds or even two thousand feet 
Fig. 2. — Dikes in the wall of the inner gorge of the canon, as shown in transverse vertical sections in the wall of a lateral 
amphitheater. Toroweap. 
through solid limestone, with one edge of it protruding laterally out of the 
face of a scarp wall. And if the chasm had approximately its present 
depth the lava would surely have burst from the face of the wall at or near 
the bottom. In no way does it seem possible to account for them in their 
present positions and relations except by assuming that the depth and width 
of the gorge was then but a small fraction of the present dimensions. We 
know that basalts play curious pranks sometimes, but they always keep 
withiu the limits of possibilities. On the other hand, the chasm must have 
had some notable depth, for in a few places are seen remnants of tufa beds 
descending from the cone over the crest of the side gorge and several hun- 
dred feet down into it. Wliere they occur the solid strata beneath them are 
not scarped, but are beveled ofiF to a moderate slope, allowing the tufa beds 
to repose upon them at an angle of about 23°. These tufas, apparently, 
were formed in the usual manner about the vent by the fall of lapilli and 
