All soils are produced by the breaking down of the mountains under the influence of weathering. The broken down rock is washed into the hollows and lowlands by the rains and floods of melted snow, and there forms soil. Soil may, therefore, be defined, in a general way, as pulverized rock. Nearly all rocks contain the elements above enumerated as being essential to a plant's life; and nearly every soil will, consequently, be in possession of them. Rocks, however, in being subjected to the action of weathering, undergo other changes than mere pulverization. The potash, lime and other plant foods held by a rock are in an insoluble condition, and can not be taken up with any ease by the plant roots. As the rock is pulverized in the process of weathering, it is also made more soluble, and the juices of the plant roots can then absorb the needed foods with greater facility. This process of making the soil more soluble, continues while time lasts, and every year will find the soil more soluble than the year before, if there are no opposing actions. Therefore, the fertility of a soil is determined not only by the quantity of plant food it contains, but also by the condition of solubility the soil constituents are in. According to the facts above given, it would be fair to infer that a soil becomes more fertile with every year that passes. This would be the case were it not for opposing tendencies. First, the crops grown upon a soil remove considerable quantities of mineral plant food. This alone would not seriously affect the fertility of a soil did not other forces act in conjunction with it. The most important cause of lowering the fertility of soils is the loss of plant food due to drainage. In districts of abundant rainfall, as, for instance, the Eastern United States, sufficient rain falls to soak the soil thoroughly and to drain through and go off as drainage water. The water, in passing through the soil, will dissolve, as far as it can, the soluble ingredients, including the plant foods, and carry them away into the rivers and finally into the ocean. This action, continued for many years, will rob the soil to feed the ocean; in fact, the saltness of the ocean is due, largely, to the substances washed out of the soils. Most of the poor soils of the world have been rendered infertile in this way. If, on the other hand, only a small quantity of rain falls upon the soil--an amount sufficient to soak the soil without draining through--the water will gradually be evaporated back into the air, and there will be no loss of plant food. In such a district the soils, if they are treated right, become richer year by year, even though subjected to tillage, if the tillage be according to our best knowledge.