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. Ill, Atlas, sheet IX., 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 lava 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 othei's, would be included in the special study of the Toquerville 

 district, which may be so highly commended as a sixbject 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 exploratiou 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 



