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Show 177 Saline efflorescences composed of chloride and sulphate of sodium are the commonest ; less frequent is the occurrence of sodium carbonate; still rarer are borates. At one place, Coyote Hole, Inyo County, the deposit of borate of soda is of considerable dimensions. Extensive deposits of nearly pure rock- salt are found in the valley of the Virgin River, about 10 miles above its junction with the Colorado. Geological circumstances point toward their Quaternary age and indicate that Bowlder Cafion is older than these deposits. Before the cutting through of the Black Canon range, i. « ., before the completion of Bowlder Cafion by the Great Colorado, the water must have accumulated in a large lake 40 miles in width, and bounded in the east by the pleateau through which now the Grand Cafion extends. It is upon the bottom of this ancient freshwater lake that the large rock- salt deposits are found. These conditions render it highly probable that their formation took place after or by the receding of the Quaternary ocean, and that Bowlder Canon was in existence before the submergence of the country at this period, which becomes evident also by the characteristic position of the Quaternary conglomerates within the head of Bowlder Cafion and in the neighboring washes. On the other hand, evidence is furnished, by erosion, that the cafion is not older than the Tertiary epoch, for there are dikes of basalt cut through so perfectly even with the inclosing syenite at quite a considerable distance above the river, that we must conclude the basalt- dikes existed before the erosion of the cafion; that is, the age of the cafion has to be referred to the later Tertiary. The lapse of time required for the completion of the great canons of the Colorado is, after all, not so great as one would be inclined to estimate at first sight. If we take the erosion of Niagara Canon, that is, the retrocession of Niagara Falls, as an example, which amounts, according to Hall and Lyell, to 1 foot a year, a period of one and a half million years would be required to complete the Grand Canon of two hundred and eighty miles in length. Not less than by the saline efflorescences and salt- deposits is attention arrested by the conditions of the Quaternary conglomerate, it being exceedingly coarse and occupying frequently localities far distant from the mountains that contributed the pebbles. This fact can hardly find any other explanation than that powerful currents agitated the waters of the comparatively shallow Quaternary ocean and distributed the coarse material over large areas. These conglomerates acquire a considerable thickness, as elucidated by the artesian borings of San Bernardino, which penetrate them for 140 feet. Neither limestone nor clay beds are Btruck by these borings, and the water rushes np as soon as the loose Band beneath the conglomerates is reached. FRESH- WATER LAKES OF THE QUATERNARY PERIOD. After the receding of the waves the country enjoyed a climate moister than that of the present day, as is indicated by the formation of a number of fresh- water lakes that left nothing but the barren clay bottom, whose numerous imbedded shells give evidence of a more numerous animated life. Owen8 Lake, now charged to such a degree with salts * that molluscous or fish life is impossible, was formerly an extensive fresh- water lake, as the recent shells in its immediate vicinity indicate. Mono Lake had gigantic dimensions, to judge from the well- defined shore- lines, 15 miles from its present margin. Soda Lake, now a barren clay flat of forbidding appearance and desolating sight, ( the saline fiats of the Mohave River,) was a large water basin, but the largest lake of Southern California existed in the Coahuila Valley, and to all appearances up to a period less than a thousand years before the present day. t Among the coarse granite-sand of its former western shores formed by the eastern slopes of the Jacinto Mountains are found millions of min ate fresh- water shells, ( Amnicola thryonia,) most delicate structures, that would long ago have been crushed between the rolling sand and have disappeared, if the period elapsed since the desiccation had been a considerable one. A calcareous crust, several inches iu thicknessand of quite fresh appearance, covers the granite of the slopes, and marks exceedingly well, by a far- stretching horizontal line, the shores of the former lake,! whose depth was about 125 feet and surface probably over 1,000 square miles. This porons crust, of the structure of a sponge, contains numerous fresh- water shells. The now dry clay bottom is covered with patches of white salt efflorescences, and nothing save an occasional stunted Halostachys inter- * Should this be due to the bursting forth of mineral and thermal springs opened by volcanic forces T Lava of recent origin occurs in the vicinity and mineral springs are numerous in the neighboring Coso Range. tThe Kauvuya Indians of that region have still a tradition of the lost lake. J This region has been described before by Prof. W. Blake. See Pacific Railroad Reports, vol. 5. |