Lake Superior Paper - Evidences of Plication in the Rocks of Cananea, Sonora

The copper-beariug rock formations of Cananea, Sonora, Mexico, present conclusive evidences of extensive and sharp plication. Some of these evidences are here briefly stated. 1. There is a succession of approximately parallel outcrops of an altered limestone, alternating with dikes and masses of porphyry. The great copper-ore deposits are in close association with these ridges of limestone, which trend northerly and southerly and stand nearly vertical. This parallel succession is so well-defined that the management of the mines has, for convenience, recognized and named five zones, known from the chief mines, in their succession from east to west, as the " Cobre-Grande," " Veta-Grande," " Esperanza," " Capote," and " Puertocitas " belts. The intervening and separating formations are coarsely crystalline feldspar porphyries, highly basic, of light color, which may be regarded as intrusive and, in part at least, as the cause of the metamorphosed condition of the limestone. 2. These cupriferous limestone-zones are similar in constitution, are similarly charged with copper-ore (in association with quartz as a gangue, or veinstone), and are marked by similar croppiugs of gossan. 3. Distinctly folded outcrops of the surrounding strata can be observed, especially on the eastern border of the copper-bearing district north of the Democrita ground, and not far from the Veta-Grande. 4. The limestone ridge adjoining the Veta-Grande ends a short distance north of the mine, and appears to be the extretne end of a synclinal trough. 5. The Capote limestone, the most western of the croppings of the central copper-bearing area, is contiguous to stratified sandstones and quartzites, uplifted at high angles, but showing an easterly dip. The Capote limestone is apparently conformable