236 
FRAMEWORK OF ARIZONA 
tageously compared with the groupings so apparent in the north, 
in British Columbia. ‘Eventually the terms Chuar and Unkar will 
have to give way and be dropped, as the true serial relations of the 
sequence are revealed. The latest Proterozoic and the earliest 
Cambric times are believed to be unrepresented by sediments in 
the Arizona region . 
Notwithstanding the fact that the Grand Canyon section of 
the Proterozoic strata is the first to be divided and the several 
members given special geographic designations, it is not probable 
that this sequence will ultimately remain the standard one for the 
state. The thick succession of the Mazatzal Mountains in the cen¬ 
tral part of the state is more clearly defined, more complete, and 
more extensive, and its subdivisions will thus take precedence. 
In order to vizualize properly the Arizona Paleozoics it turns 
out that they all have to be adjusted to an old unconformity 
plane at the base of the Devonic section. This is best accomplished 
not in the Grand Canyon but elsewhere. In the Grand Canyon 
section Newberry, so early as 1861, declared Devonic beds to be 
present, yet it is not until long afterwards that the actual finding 
by Walcott of unquestionable fossils of this age places the actual 
occurrence beyond peradventure. But the Devonic sediments of 
this locality are discovered to fill only shallow swales and pockets 
in the tops of the eroded Cambric formations. The stratigraphic 
significance of the observed features and the basal hiatus are usu¬ 
ally entirely overlooked and are unevaluated. 
Thin as is the Devonic section in the Grand Canyon, and incon¬ 
sequential as seems the local discordance in sedimentation there, 
the latter horizon proves to be one of the most important uncon¬ 
formities in the entire region and of the whole Paleozoic section. 
Even at the point at which the Siluric limestones begin to appear 
in the eastern part of the state under the Devonic beds, there is evi¬ 
dently missing at least three great rock series, the time equivalency 
of which perhaps surpasses the span of the entire Devonic Period. 
This seeming insignificant discordance in sedimentation in the 
Grand Canyon is, therefore, thrice one of major consequence. 
Recognizing the prime stratigraphic significance of the uncon¬ 
formity at the base of the Devonic succession, and platting the 
other formations around this central line in vertical section' (plate 
xvii), the various Paleozoic terranes heretofore illy correlated 
