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Show 179 The questions arise: 1st. Whence was the manganese derived? 2d. How was the coating produced f Chemistry points to the widely- spread pink and amethyst colored granites, gneisses, limestones, and sandstones, and leads to the conclusion that the manganese present in the state of proto and sesqui oxide in these rocks furnished also the binoxide for the black coating of the Quaternary drift, by becoming dissolved as carbonate of manganese upon the disintegration of the rocks, covered partly with the water of the slowly-receding, shallow ocean, and by being deposited afterward upon the rocks of the ground, where it changed gradually from the state of proto and sesqui oxide to the binoxide by the influence of air and sunlight.* This fact forms an analagon to the production of coatings of oxide of iron by waters that contain ferrous carbonate; and can be observed on a grand scale at localities where earthy carbonate of manganese is found. B. von Cotta mentions one instance of this kind jn his " Treatise on ore deposits " occurring iu the gold- bearing regious of the Rhine : " Widely- extended strata of those slates consist largely of white or reddish rhodonite, ( carbonate of manganese,) which, when exposed to the air, turns as black as coal, since it becomes inorusted by a very thin layer of manganite." There can hardly exist a doubt that the pink color of the lime and sand stones of the Mohave Desert also is due to the manganese derived from the granites, t while, on the other hand, the volcanic rocks may have contributed their share in coloring the Quaternary drift. At Mountain Springs, in the Cerbat range, a pink chalcedony was observed that most probably has derived its manganese from the trachydolerite of the vicinity. That the pink color of the palneozoic limestone of those regions is due to manganese, was easily proven by dissolving a piece iu hydrochloric acid, adding excess of ammonia, filtering off the hydrated oxide of iron, precipitating the filtrate by sulphide of ammonium, and fusing the precipitate with soda and a little saltpeter. THE ERUPTIVE FORMATION. The eruptive activity, once so extensive in the countries west of the Rocky Mountains, appears to have reached its summit in California, or, more generally mentioned, in the countries of the Pacific coast. Here appear to exist unusually favorite regions of the operations of the Plutonic powers; for the most ancient as well as the most modern geological records tell of convulsions and outbursts of molten masses, and even at the present day Pluto manifests his subterranean energy by frequent shocks and earthquakes. There is no mountain- range of Southern California free from eruptive material, which either occurs in injections and dikes, or forms entire hill- ranges and mountains, nor are there auy known rocks that do not find a representative here. From the oldest erupted gneiss, syenite, diorile, up to the porphyries, trachytes, and basalts, the series is complete. In coloration, in structural character, no greater variation could be found, and in the bursting, uplifting, and dislocating of sedimentary rocks, a geological genius could not be more productive in furnishing designs. Eruptive gneiss.- Near the northern end of Coahuila Valley, rise abruptly above the sandy piaiu two hills 20 to 30 feet in height, of highly crystall. ne limestone, of either primitive or palaeozoic age, whose strata dip at an angle of 36° to 40° to the eastward, traversed by a dike of a Highly micaceous gneiss 1 to 2 feet in thickness. The rocks are at the contact- surfaces very friable and metamorphosed. The intrusive gneiss shows by the position of its mica- plates a stratification parallel to the limestone layers, indicating the effect of pressure during the consolidation of the injected rock mass. Eruptive syenite.- A great portion of the eastern slopes of the Buena Vista Mountains, the portion of the Inyo range in which the mining- town Cerro Gordo is situated, is composed of syenite, to whose eruption is not only due the remarkable displacement of strata of palaeozoic limestone on the eastern slopes, ( see Fig. 2,) but also the disturbances produced on the west side of the mountains, the strata of slate, sandstone, and limestone standing on end for a distance of several miles. Section for the eastern slopes of Buena Vista Mountain 3 miles east of the mining-town of Cerro Gordo. Strata of palaeozoic limestone, P, standing npon their vertex, and forming with each other an angle of about 80°. £, eruptive syenite, entering the strata like a wedge. * Mr. Joy, geological assistant of Division No. 2, mentions in his notes a hot spring near Montairs ranch, California, whose waters deposit a black coating over rocks, probably due to the formation of binoxide of manganese from the protocarbonate eld in solution by the spring- water. t Pink granites were observed at the Riverside Mountains, Monument Mountains, Chukawalla Peak, Mohave River Valley, Payute range, and other localities. |