300 
MAZATZAL QUARTZITE 
cracks. The thickness of these shale lenses varies greatly. One 
observed in the bed of Pine Creek, in the Natural Bridge area, 
is 150 feet in thickness. 
Thin slices of the quartzite shows under the microscope that 
the rock is made up of grains consisting almost entirely of quartz, 
which are cemented by siliceous matter, along with some limonite. 
These grains are sharply angular. Some secondary enlargements 
are noticeable. Thin sections of the shale show it to consist of 
extremely fine, almost ultra-microscopic particles, among which is 
abundant red iron oxide. The poikolitic character is probably due 
to the unequal diffusion of the iron oxide. 
Massiveness of bedding in the quartzite is the rule, rather than 
the exception, and because of this fact jointing is usually quite 
persistent, giving very rugged expression to the topography. 
In the Natural Bridge and Del Rio areas especially, and some¬ 
what also in the East Tonto Creek district, the strata display 
marked folding and faulting, of Pre-Cambrian date for the most 
part; but in the Mazatzal Mountains and the Tonto Creek areas 
the beds are normally unaffected by orogenic compression. 
The basement complex consists usually of schists, in great 
variety having been derived from both sedimentary and igneous 
rocks. It is cut by intrusives, for the most part Pre-Cambrian 
granites and diorites. Frequently these intrusives constitute the 
basal rocks over large areas. It is probable that they are, in the 
main, related to the granites of the Bradshaw Mountains. Fre¬ 
quently the schists contain intercalated quartzitic members of var¬ 
iable but considerable magnitude, such as those noted in the Del- 
shay Basin, and around Four Peaks to the southward. Such 
quartzites, however, are not to be confused with those, younger 
than those genetically associated with the schists, which are here 
described. 
Overlying the basal schists and granites in conspicuous uncon¬ 
formity is the quartzitic formation under consideration. In the 
Natural Bridge area this unconformity is further emphasized by 
a well-defined, basal conglomerate, which contains pebbles of the 
schists, quartzite, granite, red slates, jasper, and aplite. It is not 
observed in the Mazatzal Mountains sections; and it is not ex¬ 
posed in the Del Rio district. 
