Page:Popular Science Monthly Volume 21.djvu/364

352, for four and a half to five feet, holds unnumbered crystals; at that depth they suddenly and abruptly cease. Abundant explorations demonstrated that none were to be found any lower, and the daily working came to recognize the fact as established. The mud below that was saturated with the salts of soda, such as held by the water of the lake, but no distinct crystals existed.

The crystals of borax, in the upper portion, were removed by means of coffer-dams. Each dam consisted of a box, without top or bottom, four feet square and six feet deep, made of thin boiler-iron, suitably stiffened with surrounding bands of heavier iron. These dams, suspended above the water, between large pontoons or floats, were allowed to drop suddenly, whereupon their force of descent, drove the sharp lower edge down through the soft mud and into that which was sufficiently firm and tenacious to resist the impact, and to render thus the iron walls of each a true coffer-dam, from which the entire contents could be easily removed.

The water was first pumped or bailed out, till it became too thick to flow easily, and the remaining mud was lifted in tubs, in true mining style, and thrown into large troughs, where, being subjected to constant agitation in streams of the lake-water, it was washed away, the borax being retained by its superior gravity.

No crystals were found until from twelve to fifteen inches in depth of the most fluid mud had passed away. The mud then began to feel "gritty," as the workmen expressed it, the "grit" consisting of multitudes of most exquisitely perfect minute crystals of borax. These crystals, like all those in the lake, were lying loose, detached from each other, attached to nothing by the base, and consequently perfect at both ends. It is not meant by this that every crystal was absolutely complete in every angle, but that they all had the tendency to the theoretical type, symmetrical at each end (a form which in artificial crystallization we scarcely ever reach, except by accident), and that many of them showed the type in full perfection, such as no model could excel or equal.

With every descending inch through the mud their size increased; the "grit" soon became "sand," in a few inches farther crystals were very manifest to the eye, and shortly a "layer" was reached. It is true that in some places no "layers" occurred, the crystals being scattered at random through the mud. But in most instances when from twenty-four to thirty inches of surface-mud had been removed, and the crystals had attained a length of one fourth to one half an inch, one or more "layers" would be found within the four feet square of the coffer-dam. In these "layers" the crystals were so closely packed as to have no mud intermingled with them; they were nearly as clean as though recently washed in clear water, lying closely stowed and loose, like pebbles on a beach. A "layer might be one to four inches thick and two feet, more or less, in length, surrounded on all sides by