Page:Popular Science Monthly Volume 85.djvu/144

Rh the decomposition of bat guano. By leaching of the soluble salts from the guano, the nitrates are removed and may be concentrated in other parts of the cave or distributed elsewhere.

Because of their solubility, it is not to be expected that any large accumulation of nitrates can take place excepting in protected places such as caves, or in arid countries where there is very little rain. In such countries, however, there is very little vegetation, and consequently the organic processes which are of such importance in bringing about fixation of nitrogen in humid countries are able to operate to a much less extent in desert regions. We thus find that in the soil of such regions the total nitrogen present is usually much less than in soils which support a good vegetation.

On the other hand, the soils of desert countries have marked nitrifying powers, with the result that a large percentage of the nitrogen actually present is converted into nitrates. Furthermore, owing to the low percentage of organic matter present and to the porous nature of desert soils the anaerobic dentrifying bacteria are not so active in changing nitrates into free nitrogen, while the lack of vegetation prevents their convertion into protein nitrogen. The nitrates which are formed are thus enabled to accumulate, and either remain in the soil or are transferred by underground waters to other localities where they may be concentrated by evaporation of the water at the surface of the ground. If there has been any introduction into desert localities of organic matter from external sources, as may be brought about by the droppings or remains of animals, the accumulation of nitrates may be correspondingly increased. It thus happens for the reasons given that the largest nitrate deposits are found in desert regions.

In this country few nitrate deposits are to be found apart from those of cave origin. The most extensive so far known occur in San Bernardino and Inyo Counties, California, along the shore lines or bed beaches of what was supposed to be a former sea, but which is now geologically known as Death Valley. The region popularly known as Death Valley is that portion of the valley proper which is below sea level. The territory covered by nitrate beds has been estimated to cover an area of about 35,000 acres. Through erosive agencies the clay beds in which the nitrates were deposited have been worn into buttes and ridges of characteristic shape and color. The hills so formed vary from only 50 feet high to over 300 feet. Samples taken from the niter-bearing strata in the hills, and exposed by erosion, vary all the way from a trace to more than 50 per cent, of nitrates. It is generally agreed that these deposits have not been formed in situ, but have resulted from the concentration of nitrates formed from the decomposition and nitrification of animal and plant life which must have existed in the region at the time that the valley was filled with water. Owing to the limited distribution of these