DAVIS: THE GRAND CANYON OF THE COLORADO. 159 



come especially under my observation. In referring to these areas un- 

 der the names of the Grand cauyon district, the High plateau district 

 (these two together making a large part of the Plateau province), and 

 the Great basin province, it must be understood that the existing 

 topographical features are of relatively modern origin, that altogether 

 different topographies prevailed in earlier periods, aud hence that the 

 names here used will serve chiefly to designate areas and not forms. 

 The Great basin province was for a time a lofty mouutaiu region ; the 

 Grand canyon district was a district of broad plateaus ; and the High 

 plateaus were part of a great interior basin. Most of the statements 

 concerning these districts are, it is believed, well assured, but some of 

 them are open to the serious criticism of departing from the conclusions 

 reached by the original observers whose observations are quoted. This 

 section as a whole must therefore be largely speculative ; yet the 

 speculations have some recommendation, in that they do not contradict 

 recorded observations, and that they combine to form a mutually con- 

 sistent scheme of geological events. These speculations may at least 

 serve as targets toward which discussion may be aimed, even if they 

 do not present any ultimate truth. 



Tlie Geological History of the Region. — The Basin range province 

 has been disturbed by post-Jurassic plication and by late Tertiary fault- 

 ing. King wrote that the Great basin " was a region of enormous and 

 complicated folds, riven in later time by a vast series of vertical dis- 

 placements. . . . The Great basin . . . has suffered two different types 

 of dynamic action : one, in which the chief factor evidently was tangen- 

 tial compression, which resulted in contraction and plication, presumably 

 in post-Jurassic time; the other of strictly vertical action, presumably 

 within the Tertiary " (pp. 735, 744). Dutton makes a similar state- 

 ment : " These [Basin range] flexures are not . . . associated with the 

 building of the existing mountains. . . . The flexures are in the main 

 older than the mountains, and the mountains were blocked out by faults 

 from a platform which had been plicated long before, aud after the in- 

 equalities due to such pre-existing flexures had been nearly obliter- 

 ated by erosion" (a, p. 47). Several passages in Gilbert's first western 

 report are of interest in this connection. He concluded " that the 

 Plateau [region] is not a unit in history and origin, and that the only 

 criterion by which it can be distinguished from the [Basin] range 

 country, is the . . . superficial one of table and ridge. . . . The 

 whole phenomena [of displacement] belong to one great system of moun- 

 tain formation, of which the ranges exemplify advanced, and the pla- 



