DAVIS: THE GRAND CANYON OF THE COLORADO. 195 
of the Uinkaret ; and the youngest flow of that volcanic field lay a mile 
to the east (Powell, a, p. 131; Dutton, c, p. 111, Atlas, sheet [X., lower 
view); we crossed it on the way down into the Toroweap, and came 
back by a trail that ascended one of the great lava cascades. A young 
ash cone stands on the tabular top of Mt. Trumbull, whose mass is but 
the remnant of a once much larger lava mesa; the young cone was pecu- 
liarly placed near its southeastern end of the mountain. A series of 
cones and black Java flows were passed in the northern part of the Uin- 
karet block, between the western scarps of the Shinarump mesa and the 
Hurricane ledge. The lava-floored valley above Workman spring has 
already been mentioned. The canyon of the Virgin just after the river 
emerges from the Hurricane ledge is cut in lava for several miles. 
A side canyon, about two miles south of Toquerville, revealed a fine 
section of a lava flow lying on a coarse gravel which partly filled a small 
valley, all shown in a single section. These latter items, along with 
many others, would be included in the special study of the Toquerville 
district, which may be so highly commended as a subject for a summer’s 
field work. 
Summary. 
_A high degree of consistence among: the consequences of various 
associated theories is justly regarded as strong proof of the correctness 
of the theories themselves. Each of the earlier students of the Grand 
canyon district probably reviewed his conclusions to see that they were 
mutually consistent, and published only those that survived this test. 
As the progress of exploration and the advance of earth-science furnished 
more and more items in the sequence of events that make up the history 
of the district, the interlacing of more and more elements seemed to give 
at once greater difficulty to the problem and greater certainty to its 
solution. Dutton in particular appeals this aspect of the method of 
proof, and truly the successive steps in his thesis are strongly enchained. 
Yet it now seems possible to arrange a new sequence for some of 
the events by which the present order of things has been produced : 
a sequence which differs from that announced by previous observers in 
several particulars, as presented in the concluding summary below, al- 
though still holding to the main outlines of the geological history of the 
region as presented in the several governmental reports. The question 
then arises, where shall the permanent truth be found among all these 
suggested possibilities? Further exploration, and more particularly 
detailed study of certain special problems, will in due time review all 
