MAZATZAL QUARTZITE 
307 
of the formation are shown. The exposures are especially note¬ 
worthy because of the fact that there is shown over the old Pre- 
Cambrian quartzite a younger Pre-Cambrian sequence. 
The older quartzite directly overlies Pre-Cambrian schists and 
granites, with , stratigraphic hiatus of unestimated magnitude. 
It underlies, with unconformity frequently difficult to trace, a 
younger Pre-Cambrian succession entirely different from itself. 
The Paleozoic rocks of the Plateau escarpment abut both it and 
these younger rocks. 
Exposures in Gordon Canyon, about three miles south of the 
‘T3” Ranch, show, abutting the Pre-Cambrian rocks, typical Red- 
wall limestone overlying with apparent conformity about 100 feet 
of brown' flaggy, cross-bedded, coarse sandstone, which may rep¬ 
resent either the Cambric Tapeats sandstone or a sandy base of the 
Carbonic Redwall Limestone. 
This young sequence of Pre-Cambrian strata consists of grey 
to red-brown quartzites, about 250 feet in thickness, overlain 
by limestones 60 feet thick. 
This younger quartzite formation, often intruded by diabase, is 
often apparently conformable above the Mazatzal section except 
for the presence of a basal conglomerate made up of strikingly 
subangular pebbles, often as large as one foot in diameter, of Ma¬ 
zatzal materials, held in a red and sparkling matrix. Above the 
•basal conglomerate are a few layers that show cross-bedding, and a 
few that show tension-cracks and ripple-marks. The quartzite 
member as a whole is characteristically thin-bedded and well 
indurated. 
The limestone member overlies the quartzite member in appar¬ 
ent conformity. It is characteristically dark to dark gray in color, 
thin-bedded, and banded with chert. It is subject to consider¬ 
able alteration resulting in the development of serpentine. Its 
observed thickness is about sixty feet. 
Much remains to be considered relative to our complete under¬ 
standing of the sedimentation phenomena like those presented by 
the Mazatzal quartzite. Some general impressions obtained seem 
worthy of brief relation; and they appear to agree best with the 
conception that the Mazatzal quartzite was laid down in the delta 
of a great Pre-Cambrian river, which emptied into a steadily en- 
