Publisher's Synopsis
This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1912 edition. Excerpt: ... APPENDIX III GEOLOGICAL SKETCH OF THE PAPAGUERIA BY CYRUS F. TOLMAN, PROFESSOR IN MINING AND GEOLOGY, UNIVER- SITY OF ARIZONA The two groups of formations most extensively developed in the Papagueria belong respectively to the most ancient of rocks and to those formed during geologically recent times--to the pre-Cambrian complex on the one hand and to the Tertiary-Quaternary group on the other. This great area has been studied only in spots by geologists, and therefore detailed knowledge of the formations is lacking, and they have not been matched up with those of other and better known portions of the country. As far as present knowledge goes, the older group consists of gneisses, schists, slates, crystalline limestones, and coarse grained granites--the granites and granite-gneisses being most abundantly developed in the south-western portion. The group of younger rocks is made up chiefly of extrusives; volcanics represented by andesites, rhyolites, rhyolite-tuffs, and basalts. These are mentioned in the order of eruption as shown in the majority of localities. The most recent of the basalts, the extrusion of some of which may have continued into historic times, form in cases perfect volcanic cones, but the older lavas and most of the basalts appear as remnants of flows in fault blocks, or better as fault strips, these upturned blocks and strips forming many of the volcanic ranges. Less widely distributed than the two groups mentioned above, but important throughout the Arizona Copper Fields as ore carriers, are the Paleozoic Series of limestones and quartzites. These are found in the Papagueria in the eastern and southern ranges; for instance, in the Tucson Mountains, the Silverbell Mountains, the Sierrita Mountains, in the Vekol...
