39+ A HISTORY OF CHILE The calicheras lie near the surface, from one to ten feet below, and to reach them small excavations are made. Blasting powder is put under the raw nitrate and the ground thus broken up for a considerable dis- tance, then the caliche is separated from rock and rub- bish as much as possible and loaded into sheet iron mule carts, in which it is transported to the crushing mills. It is then bruised between rollers, dissolved and deposited in tanks and crystallized in vats, from which it is drawn off much as salt would be, and sacked for transportation. Beside the nitrate of soda there are the accessory salts found in it, potassium, magnesium, gypsum, and iodine. Caliche itself is crystalline in structure, solu- ble in water, and has a slightly saline taste. The ori- gin of the deposits is somewhat in doubt, but appears to have been the result of decomposition of seaweeds at a time when this part of the continent was under the ocean. With the upheaval of the land salt water lakes were formed, and, with the evaporation of the water, nitric acid was generated by the decomposition of the seaweeds and this, acting upon shells and limestone, formed nitrate of calcium, and nitrate of calcium unit- ing further with sulphate of soda, left also by the evap- orating sea water, gives the result, nitrate of soda and sulphate of calcium. The beds have been preserved in their present condition for ages, because of the fact that rain seldom falls on this part of the coast. Moist- ure would dissolve and destroy the product. The export of nitrate of soda amounts annually to more than twenty million Spanish quintals, of one hundred pounds each, and this is valued at thirty mil- lions of dollars. The state receives from this export over twenty millions of dollars annually, an amount exceeding all the general import duties, and in the
