FRAMEWORK OF ARIZONA 
235 
other two. The Archeozoics may also be conspicuously represented 
by the unaltered granites, diorites and other plutonic masses which 
everywhere intrude the most ancient crystalline schists, and togeth¬ 
er with the latter are sharply cut off by the unconformity plane at 
the base of the Proterozoic clastic column. 
Analysis of Arizona’s general rock-section gives clue to the de¬ 
velopment and meaning of the great pre-Cambrian sequences of 
sediments which especially distinguish the Little Belt and Selkirk 
mountains far to the north. That these old strata, as they are 
developed beyond the southern extremity of the Rocky Mountains, 
have never received the attention that they merit, is as true of 
Arizona as it is of New Mexico. Although the Grand Canyon 
section of the pre-Cambrian sediments is not so important, those 
of the central part of the state, as recently disclosed in the Cata¬ 
lina and Mazatzal Mountains, compare favorably in magnitude, 
variety, and excessive thickness, with the prodigious developments 
of British Columbia. Whether Arizona rocks resolve themselves 
into the same great successions reserved for them in other parts 
of the continent remains to be determined. The general perspec¬ 
tive is certainly no more perplexing than was that of the Transi¬ 
tion (Paleozoic) rocks of England a century ago. Today the 
basal part of this sedimentary column offers the most promising 
field of endeavor for new and large results that the world affords 
in stratigraphy, novelty, and backward extension of the sedimen¬ 
tary record into the gulf of time. 
Proterozoic sediments with little signs of alteration from the 
original induration find tremendous development in the Arizona 
area. A thickness of between two and three miles is already 
known; and it is probable that ultimately the column will expand 
to several times this measurement. Several lithologic segregations 
are differentiatable, but the serial and periodic groupings still re¬ 
main to be exactly delimited. The rocks of this age are mainly 
sedimentaries. Since they are pre-Cambrian in age they are fre¬ 
quently alluded to as Algonkian. But the latter title is now so 
Very elastic that it really means nothing. As originally proposed 
the term covers all pre-Cambrian sedimentaries, under the mis¬ 
conception that the beds form a circumscribed sequence every¬ 
where overlying the primeval crystalline complex. 
Tentatively, at least, the periodic subdivisions may be advan- 
