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Page:Popular Science Monthly Volume 21.djvu/371

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of dotted spots, individually of no great extent, scattered over the desert regions east of the Sierra Nevada. Most of them are without designation, but a few are marked "Soda Flat," "Salt Marsh," etc. They all have probably a common origin; they are places which long ago (how long we can not tell) were covered with water, since removed by solar evaporation. Each consists of an extent of entirely flat surface of dried mud, sometimes absolutely bare, sometimes covered with saline deposits. It had been known for years that these deposits were both what is there universally called "alkali" (carbonate of soda) and salt. But it was not until 1871 that much attention was drawn to the fact that several of them contained also deposits of borates, though published mention had been made some time earlier that these existed there.

The number of these "marshes," which are marked by borate deposits, it is impossible to state, as so large an extent of that arid region remains as yet very imperfectly known. A sketch of one, however, gives the characteristics of all.

One of the largest is known as the "Columbus Marsh." It is situated in Esmeralda County, about two hundred and fifty miles nearly due east from San Francisco, and about one hundred and sixty miles south of Wadsworth, on the Central Pacific Railroad. The portion last abandoned by the water, and now covered by saline deposits, extends about ten miles from east to west, and three from north to south, with an extension on the south into Fish Lake Valley, forming an arm fifteen miles long by one to three miles wide. Not all parts of this extent are equally rich in salines, neither is the character of the deposits the same at different parts, though it must have formerly been covered with one sheet of water, of presumably a uniform quality or nearly so.

A space of several hundred acres in one part, for instance, is covered with a crust of chloride and carbonate of soda, through which the foot breaks at every step; but the black mud beneath is filled to the depth of six to twelve inches with borate of lime aggregated in nodules, which, when broken open, show a beautiful pearly-white mass of satiny luster. These are the ulexite, and are commonly called "cotton-bolls." They can be picked out by hand like the kernel of a nut, separating clean and clear.

Immediately adjoining the ground thus rich in ulexite is a wide stretch barren of everything, except a little chloride and carbonate. Just beyond this come five or six hundred acres, thickly covered with borate of soda, so little contaminated with sand or anything else as to crystallize out, by simple solution, eighty per cent of its weight in pure borax. Over vast extents of this surface I have seen the crude borax in its granular, semi-crystalline form lying from fifteen to twenty-four inches in depth, while, at the distance of a quarter to half a mile, the borate of lime was in similar abundance. The supply of borax