MAZATZAL QUARTZITE 
303 
A notable angular unconformity exists also between the Mazat- 
zal quartzite and the succeeding Paleozoic strata, for the latter 
often abut the former in a manner indicating a hilly character of 
the old land surface. Of this later sequence, the only formation 
of immediate interest in connection with our quartzite is a Mid 
Cambric sandstone — the Tapeats sandstone of the Grand Canyon 
region. 
The Tapeats sandstone contrasts strongly with Mazatzal quart¬ 
zite and is especially distinguished by being less indurated, and 
by its medium-bedded to flaggy structure, coarse-grained to almost 
pebbly texture, and the rusty to deep red coloration. In thick¬ 
ness the formations run from a few inches to over 100 feet. The 
component sand grains are generally well-rounded, or ellipsoidal, 
in shape, and the pebbles attain sizes over an inch in diameter. 
They are predominantly white quartz, but there are frequently 
present variable amounts of red jasper, feldspar, quartzite, schists, 
and granite. The cementing material is siliceous, and with it is an 
abundance of limonite. 
Regarding the general terranal relations it is to be noted that 
the Paleozoic and later rocks abut the folded and faulted Pre- 
Cambrian quartzites which are being considered. Later faulting 
and folding also somewhat disturbe the Paleozoic beds; but most 
of these folds appear to be fractured at their crests and troughs, 
so that nowhere is any steep dip far removed from the vicinity 
of a fault. This relation gives rise to step-like fault-blocks, with 
which the usual consideration of the phenomenon of drag might 
in some cases easily indicate on casual inspection a wrong direction 
of movement. No definite data are obtainable relative to the 
geological age of the later faulting, beyond the circumstance 
that Tertic strata are seldom affected by it, an exception being 
in the Del Rio region, where the lava flows may be earlier than 
those in other areas. 
The main body of the Pre-Cambrian quartzites, that portion 
exposed in the northern partion of the Mazatzal Range covers 
an area of over forty square miles. Beginning at North Peak, 
it extends south and southwestward to a point about three miles 
south of the Mazatzal Peak. 
The beds rest on granites and schists in notable unconformity. 
