_White_ soils, or more properly those having very light gray tints, are not usually looked upon with favor, especially in the humid region. The causes of the unfavorable judgment current among farmers in respect to white soils has already been partially explained in the discussion of the black and red tints. The light color means the scarcity or absence of both humus and ferric hydrate, and usually implies that the soil has been subject to reductive maceration through the influence of stagnant water; reducing the ferric hydrate to ferrous salts, oxidizing away the humus, and accumulating in the form of inert concretions most or all of the lime, iron and phosphoric acid of the soil mass (see chap. 3, p. 46, chap. 10, p. 184). The term “crawfishy,” so commonly applied to white soils in the eastern United States, expresses well the usual condition of the white soils of that region; which are very commonly inhabited by crayfish, whose holes reach water a few feet below ground, and are surrounded on the outside by piles of white subsoil mixed with “black gravel” or concretions of bog iron ore. It is needless to say why such lands cannot command the favorable consideration of the farmer; they cannot as a rule be cultivated without previous drainage, and even after that will usually prove unthrifty, “raw,” and in immediate need of fertilization by green-manuring, and the use of phosphates. In the arid region, lands of this character are of rare occurrence, while (as has been explained above, chap. 8, p. 135), the light gray or “white” tints are there a very common characteristic of even the very best soils. It is true that they are poor in humus and in finely diffused ferric hydrate; but their “light” texture renders the presence of humus for this purpose less needful, and as stated elsewhere (see chap. 8, p. 135), the high nitrogen-content of arid humus renders a smaller supply adequate for vegetative purposes. As to iron, its presence being more important as a sign of good drainage and aeration than directly, its absence from soils of great depth and loose texture is of no consequence; especially when the heat-absorption which it favors is not only not needed, but is usually already in undesirable excess during the hot summers. _White Alkali Spots._—In the valleys of the arid region, however, _very_ white spots commonly indicate the prevalence of alkali salts, and to that extent are an unfavorable indication; especially when coupled with the occurrence of black rings or spots, which indicate the presence of black alkali or carbonate of soda (see chap. 22). CHAPTER XVI. CLIMATE.