TniO OEAND CASfON DISTRICT. 
()(i 
referred to lies along a portion of its southeastern shore. Great masses of 
Triassic and Jurassic beds are turned up along this belt with every indi- 
cation of a shore-line: conglomerates, coarse sandstones, and grits, much 
faulted and flexed, and showing those peculiar unconformities produced by 
the sinking and flexing of overloaded littoral beds, as the coarse detritus is 
rapidly piled up. Beyond is the greatly ravaged platform of Archaean and 
Paleozoic rocks. It has been shown in the preceding chapter that these 
formations and indeed the entire Mesozoic slowly attenuate as they recede 
eastward and east-southeast from this shore line. The extension of the 
shore of the Mesozoic mainland towards the west or southwest remains to 
be sought. It has never yet been explored. But another portion of the 
coast of the Mesozoic sea important for our purposes may be pointed out. 
Starting from the base of the Vermilion Cliff's and proceeding southward 
to the Grand Canon, we find no traces of a shore-line. If any more recent 
than Carboniferous time had existed in the interval, it would have left 
vestiges, and these vestiges could not have escaped our observation. In 
the extension of the formations of the terraces, therefore, we find no logical 
halting place north of the Grand Canon. In all the interval the conditions 
of the problem are quite unchanged. The logic which extends them a 
half mile extends them to the brink of the chasm. But even here the 
problem persists. The mind leaps across the abyss only to find the object 
of its pursuit receding ever southward. At the San Francisco Mountains 
the pursuit is not ended. Here are several AEtnas surrounded by a host of 
young craters which have deluged the country Avith rhyolite and basalt, 
hiding the strata beneath. Beyond these Phlegraean fields the Carbonifer- 
ous beds reappear as before, stretching away southAvard and sensibly hori- 
zontal until at last they come to a sudden end in the Aubrey Cliffs. These 
cliffs face southward and southwestward, overlooking a region of totally 
different character from that of the Plateau Province. It is a sierra country 
quite similar to the Great Basin. It discloses a rugged platform of Archaean 
rocks, here preserving a few old rags of loAver Cai-boniferous strata, there 
covered with cumbrous masses of rhyolite and irregular slops of basalt. 
It is bent, warped, shattered, faulted, and flexed; with short misshapen 
