248 
FRAMEWORK OF ARIZONA 
of clayey and sandy beds known in recent years as the Mancos 
shales. Until these shales are carefully subdivided throughout 
their range in accordance with their general lithologic and biotic 
characters it is perhaps useless to attempt to distinguish the sev* 
eral units as displayed in this part of their areal extent. It may 
be, that after the faunas are carefully worked out, the same sub¬ 
divisions may be recognizable as on the east side of the Rockies. 
The Montanan series is the great coal measures sequence. Thick 
coal-bearing shales lie between thick, massive sandstones. Al¬ 
though relatively unimportant in Arizona, in the neighboring states 
of New Mexico, Colorado and Utah, the series furnishes the larg¬ 
est coal tonnage on the continent. Montanan shales form the sur¬ 
face rocks of much of the northeast corner of the state, and conse¬ 
quently recent erosion removes much of the once much more ex¬ 
tensive formations. 
With the Cretacic strata eroded down to the middle level of the 
Montanan series, two great superior series, the Lewisian and the 
Laramian sections, are entirely unrepresented within the bound¬ 
aries of the state. This erosion of the Late Cretacic strata is not 
all referable to modern depletion. Early Tertic erosion and re¬ 
gional planation are also strongly in evidence. This is especially 
well displayed in the Chuska Mountains of the northeastern corner 
of the state, on the New Mexican boundary. These elevations are 
mainly Tertiaries laid down on a peneplain which is worn out on 
the basset edges of the Cretacic formations in the Defiance mon¬ 
ocline. 
Arizona borders one of the great Tertic successions of the con¬ 
tinent; yet only a small part of it extends into her own domains. 
With the introduction of Tertic times in this region epirotic de¬ 
position takes the place of marine sedimentation. Provincial suc¬ 
cessions become restricted and the sequences of the different basins 
have little in common. The earliest Tertic beds, earlier than any 
other known on the face of the earth, that are so well developed 
in New Mexico and in Colorado, are not represented by deposition. 
Most imposing of all Tertic successions in the state is that 
capping the Chuska Mountains, in the northeastern corner on the 
New Mexican boundary. This section is not less than 1,500 feet 
in thickness. Basal conglomerates doubtless are extensions of the 
