DAVIS: THE GKAND CANYON OF THE COLOKADO. Ill 



merit and denudation. The topographical maps prepared by Bodfish 

 and Eenshawe in 1879 are also of great service to the traveller. The 

 main conclusions of the earlier explorers are not to be disputed. The 

 great unconformities at the base of the plateau series, the enormous 

 volume of nearly horizontal and conformable strata from lower Palaeozoic 

 to Tertiary, the division of the region into great blocks by displacements, 

 either faults or flexures, trending about north and south, the great 

 denudation by which the plateaus bordering the canyon have been 

 stripped of thousands of feet of strata, the sharp erosion by which the 

 canyon has been incised in the plateaus, and the superb development of 

 volcanic phenomena, — all these great features are standard examples 

 for citation. There are, however, certain subordinate conclusions an- 

 nounced in the earlier reports which seem open to question, and it is 

 chiefly to a consideration of these debatable points that the present 

 essay is devoted. 



The following brief summary of certain aspects of the work of three 

 earlier observers may be of service to the reader. 



Newberry, geologist of the Ives expedition to the Colorado river of 

 the west in 1857-58, ascended the Grand Wash cliffs to the plateaus 

 from the deserts among the Basin ranges on the south of the river, 

 descended northward into the Grand canyon near its western end by 

 the side canyon of Diamond creek, and, ascending again, traversed the 

 southern plateaus past San Francisco mountain from west to east. He 

 recognized the fundamental crystalline rocks beneath their heavy un- 

 conformable cover of palaeozoic strata (pp. 54-58) ; he perceived the 

 importance and efficacy of ordinary erosive processes not only in the 

 excavation of the narrow canyons beneath the plateaus by the larger 

 and smaller streams (pp. 45, 46), but also in the broad recession of the 

 cliffs upon the plateau (pp. 45, 62), indeed he regarded the opening of 

 the broad upland valleys on the plateaus, such as that of the Little 

 Colorado, as " a much grander monument of the power of aqueous 

 action than even the stupendous canon of the Colorado" (p. 86). He 

 noted a " slight arching of the strata " in passing from what we may 

 now call the southern Shivwits to the southern Uinkaret plateau 

 (p. 58), and a "curve of the underlying rock " on descending from the 

 Coconino plateau (south of the Kaibab) to the platform of the Little 

 Colorado valley (p. 61) ; but he denied the occurrence of other dis- 

 placements, not only in the canyons but also along the north-south 

 escarpments, saying that "the strata of the table-lands are as entirely 

 unbroken as when first deposited" (p. 46) ; and this is not unreasonable 



