=235. Occurrence and History.=—The generally accepted theory of the manner in which potash has been collected into deposits suited to use as a fertilizer has already been described.[194] The Stassfurt deposits, which have for many years been almost the sole source of potash in fertilizers, were first known as mines of rock salt. In 1839, having previously been acquired by the Prussian treasury, they were abandoned by reason of the more economical working of rock salt quarries in other localities.[195] It was determined thereafter to explore the extent of these mines by boring, and a well was sunk to the depth of 246 meters, when the upper layer of the salt deposit was reached. The boring was continued into the salt to a total depth of 581 meters without reaching the bottom. The results of these experiments were totally unexpected. Instead of getting a brine saturated with common salt, one was obtained containing large quantities of potassium and magnesium chlorids.[196] Shafts were sunk in other places, and with such favorable results, that in 1862 potash salts became a regular article of commerce from that locality. At first these salts were regarded as troublesome impurities in the brine from which common salt was to be made, but at this time the common salt has come to be regarded as the disturbing factor. At the present time the entire product is controlled by a syndicate of nine large firms located at Stassfurt and vicinity. Outside of the syndicate properties a shaft has been sunk at Anderbeck, (Halberstadt,) which, however, has produced only carnallit, since kainit has not been found there. Also at Sondershausen, potash salts have been discovered and a shaft is now sinking there. It is thus seen that the potash deposits extend over a wide area in Germany, and there is little fear of the deposits becoming exhausted in many centuries. In this country no potash deposits of any commercial importance have been discovered; but the geological conditions requisite to these formations have not been wanting, and their future discovery is not improbable. [Illustration: FIGURE 17. GEOLOGICAL RELATIONS OF THE POTASH DEPOSITS NEAR STASSFURT.]