MAZATZAL QUARTZITE 
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naturally be deposited between the branching “arms” of a delta. 
Being extremely fine-grained and containing abundant iron oxide, 
they seem to represent reworked material derived from the more 
easily eroded iron-bearing rocks of the older Pre-Cambrian land- 
surface. 
Microscopic slides of samples taken from a dozen different 
strata of the quartzite succession did not tell much regarding de¬ 
position. This result is quite in accord with Bake, who says: 
“The composition and texture of a sandstone may furnish cri¬ 
teria regarding its derivation and transportation, but not regarding 
its method of deposition.” However, it was seen that in the slices 
examined the sand-grains making up the quartzite consisted al¬ 
most entirely of quartz, and in fragments strikingly subangular 
rather than rounded. The cementing material seems to be silica, 
and in some cases silica and limonite. It is interesting to call 
attention here to the fact that the quartzite near Fort Defiance, 
Arizona, consists of “extremely irregular angular quartz grains 
bound together by a primary siliceous cement.” It may at first 
appear surprising that no feldspar, zircon, or ferro-magnesian 
minerals, were observed in the slices from the quartzite; but the 
work of Sherzer has shown that sand grains subjected to either 
wind, water, or glacial wear, continued from a sufficient time, come 
to consist almost wholly of quartz, and each type of abrasion gives 
characteristic forms. Wind abrasion, according to him, is apt to 
make rounded grains much more rapidly than water; hence it 
seems fair to assume that the sand material making up the Mazat- 
zal quartzite never had a dune-sand chapter in its history. 
Cross-bedding, which is a conspicuous feature of most of the 
Mazatzal quartzite beds, is known to be a mark of shifting cur¬ 
rents. If of wind origin, it is more marked than the true bedding; 
but this does not obtain in the case of the Mazatzal quartzite, and 
so it indicates subaqueous deposition in proximity to a shore. The 
regularity of the cross-bedding in stratum after stratum of course 
indicates a constancy of this condition scarcely to be expected upon 
a sinking sea bottom; but the presence of delta conditions would 
naturally tend to equalize such factors of irregularity. 
Sun-cracks occur frequently in the shale and slate layers of the 
Mazatzal formation. A river at flood probably deposited these 
