170 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



accounting for lateral valleys standing five hundred or more feet over 

 main valleys whose flood plains are ten or twenty times as broad as their 

 rivers. On the other hand, the observers above named conclude that 

 the discordance is due to glacial erosion. If the former view were cor- 

 rect, then surely the discordance of side and main valleys ought to be 

 very strong in the Grand canyon, where there is no question of glacial 

 erosion, where the disparity of volume between trunk river and side 

 streams is notoriously great, and where the main valley is still so young 

 that no significant widening of its floor has been yet accomplished. Yet 

 singularly enough, the side canyons of the Colorado join the main canyon 

 at accordant levels in nearly all cases. The views from the southern rim 

 of the canyon at various points near Hance's and Cameron and Berry's, 

 and still better from the great Red-wall spur that advances northward 

 from the "copper mine" on the Grand view trail, show repeated in- 

 stances of dry or nearly dry lateral canyons, only five or six miles long, 

 which are nevertheless cut down at their months as deep as the main 

 river, if their lower course lies on the stratified rocks. It is only where 

 the main canyon narrows on entering the resistant crystallines that the 

 side canyons are held up at a discordant level ; and even there the large 

 lateral canyons seem to enter closely at grade (see detailed map, by 

 Bodfish, Dutton, c, p. 258, Plate XLIL). However discordant the side 

 and the main canyons may have been during a still earlier stage of the 

 present cycle of erosion, Playfair's law is already exemplified to-day ; 

 and if, under conditions of peculiar difficulty, some of the smaller 

 streams have not yet reached a normal relation to the master stream, 

 they only prove the verity of the law by the need of their being 

 excepted from it. 



As my own views of the canyon were only in the middle of the Kaibab 

 section and from Vulcan's throne in the Toroweap, the following infer- 

 ences to records made by others may prove pertinent in this connection. 

 Powell describes his ascent of a side canyon west of the Kaibab, and 

 mentions waterfalls in its course, one of which was one hundred and 

 fifty feet high ; but as no fall is mentioned at the mouth of the side 

 can von, it probably unites with its master in accordant fashion («, p. 92). 

 A little further down the main canyon, a stream from the north leaps 

 into the river " by a direct fall of more than a hundred feet " over a 

 "bed of very hard rock, . . . thirty or forty feet in thickness" (a, p. 93). 

 Before reaching the crystallines of the Shivwits canyon, " a little stream, 

 with a narrow flood plain, comes down through a side canon " from 

 the north. An Indian settlement was found there, with fields of corn 



