108 
THE GRAND CAllON DISTRICT. 
present in these insulated mesas of the Sheavwits we do not know, but 
we are quite confident that much more than half of it is there. The 
meaning of these outliers is evidently the same as that which we have 
deduced from the plateaus of Trumbull and Logan. The Sheavwits basalts 
were erupted at an epoch when the Permian formed the general surface of 
the plateau, and these outliers have been preserved by the lava sheets from 
the denudation which has removed the unprotected portions. (Plate IV.) 
We may now revert to the younger basalts. These have all emanated 
from cones which still remain in good preservation. Very few of the craters 
have suffered any extensive ravage from the chemical processes of secular 
decay or from the mechanical work of erosion. But now and then we find 
one which has been sapped, battered, and dissolved to some notable extent, 
though never to such an extent as to efface its more important features, or as 
to leave doubt about its nature and character. As already remarked, these 
cones cover a large extent of ground, being found from the brink of the 
chasm northward throughout a space of nearly 50 miles, and from the 
western verge of the Uinkaret to a point 20 miles east upon the Kanab 
Plateau. All around the base of Trumbull, and thence southward over the 
extreme southern part of the plateau, they cluster most thickly, often standing 
base to base, or even with confluent bases. Many of them have multiple 
vents or cups, and four or five vents in the same pile are not uncommon. 
As we proceed northward or eastward from Trumbull the cones gradually 
become less frequent and more scattered. 
The lava streams which have flowed from these cones are never very 
voluminous, compared with what may be seen in more extensive volcanic 
regions. On the southern part of the plateau some copious eruptions may 
be seen. But it is very difficult here to distinguish one eruption from others. 
In numerous places we find lava flows from a mile to two miles wide, and 
reaching five or six miles from the vents; but there can be no doubt that 
they are composed of very many streams — perhaps hundreds of them. And 
yet it is impossible to separate any one stream in its entiretj^ from the others. 
In many places the basalt has run over the edge of the plateau to the bottom 
of the Toroweap, to the esplanade of the canon, and to the floor of the 
Quean toweap Valley on the west. The passes where these lavas have 
