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 canyon 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, and 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 mountain 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. 
The 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, and 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- 
