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FRAMEWORK OF ARIZONA 
The high points in Arizona stratigraphy are the segregation of 
all of the resistant rocks in the lower part of the geological column, 
and of all the weak deposits in the upper portion, the possible com¬ 
plete absence of the Archeozoic sediments, the great development 
of the Proterozoic strata, the relative scantiness of the early Pal¬ 
eozoics, the full representation of the late Paleozoics, and the gen¬ 
eral absence of Mesozoic formations except in the extreme north¬ 
east and southeast. 
The basal complex of the Azoic rocks consists mainly of banded 
and contorted schists, slates and gneisses in great variety. In the 
bottom of the Grand Canyon, where these rocks are designated the 
Vishnu Schists, the lithologic variety is slight; but in the Tonto 
Basin, in central Arizona, many types are represented. Here the 
principal types consist of sericitic schists, greenstone schists, he- 
matitic schists, hornblendic schists, quartzitic schists, brown, red, 
and gray slates, schistose sandstones and conglomerates, laminated 
dolomites and red cherty or jaspery beds, schistose granites, dio- 
rites, rhyolites, and other igneous masses, and biotitic geneisses. 
All of these are cut by perfectly unaltered granites, diorites, peg¬ 
matites and numerous basic intrusives, representing a time long 
subsequent to the date of the regional metamorphism. 
For these oldest, thoroughly crystalline masses the designation 
Azoic is most fitting. As an alternative title Archean is the least 
objectionable. But special geographic names, as Vishnu Schists, 
Pre-Beltian eruptives, Pinal Schists, and the like, titles covering 
the entire aggregation which really has eral rank, are clearly out of 
place and utterly meaningless. Nor can any of these terms be 
properly used since Blake early designation, Arizonia slates, has 
priority by many years. The only geographic names available for 
the subdivisions are those designating the local petrographic types 
when these shall have been properly determined and their respec¬ 
tive areas have been carefully bounded. 
East of the Arizona boundary, at the southern end of the Rocky 
Mountains, in northern New Mexico, the pre-Cambrian rocks pre¬ 
sent three grand successions which are distinguishable from one an¬ 
other according to the amount of metamorphism which they have 
undergone. In Arizona only the earliest and latest of these three 
sections are yet recognizable. Possibly the median Archeozoic as¬ 
semblage is present, and it may be found merged with either of the 
