Soil
2 of the 6 encyclopedias on this shelf carry an entry for Soil. Both are reproduced below, so you can see where they agree and where they differ.
Aiton's Encyclopedia (1910)
the loose surface of the earth in which vegetation takes root. Soil is derived chiefly from rocks, but in part from the water and air. The hardest rock wears off when exposed to the weather. Changes from hot weather to cold and back again crack the surface of rocks. Water enters the slightest crack, and, expanding with frost, pries off fragments, just as it bursts a waterpipe or bulges the bottom of a pail. Lichens send tiny roots into crevices and enlarge them. Flying dust strikes against the face of a rock and chisels off more dust. Sandy water scours out furrows, each sharp grain of sand in suspension acting like a chisel to scrape off tiny stone chips. If water or air or the acids of plant roots are able to dissolve any portion of a rock, the rest is all the more likely to crumble into soil. Soil is chiefly crumbled rock. Some kinds of rocks wear and crumble into sand; others are worn and ground into clay; a third sort of soil is vegetable soil or humus. Humus is formed by the decay of plants. Some soil is almost pure sand. Some is pure clay; and some, like peat and the muck of swamps, is almost purely vegetable. A mixture of sand, clay, and vegetable soil is called a loam. If sand predominates, it is a sandy loam; if clay, a clay loam; if humus, a vegetable or frequently a black loam. Clays and sands are of any color-red, gray, yellow, vermilion, or blue,-according to the color of the rocks from which they come. Soil may be found near the rock from which it is derived, as soil at the foot of a cliff lying next the surface of a stratum of disintegrating limestone; or it may be carried thousands of miles away by streams, dust storms, and ice. The soil at the mouth of a large river has come almost invariably from rocks in the interior of the continent. Mountain chains are worn down, not infrequently a mile or two, and the soil thus made is carried down to build up the lowlands. Glaciers make and transplant enormous quantities of soil. See Sand ; Loess ; Lava
Collier's New Encyclopedia (1921)
that part of the disintegrated surface of the earth's crust in which the roots of plants ramify, and from which growing plants derive the mineral substances necessary for their proper development. Soils are formed by the disintegration of the rocks through the continued action of water and air at various temperatures, and by the accumulation of the decaying remains of vegetable organisms. In the process of disintegration water acts variously, as in the bursting action of frost, the gradual wear of running water, and the sawing, grinding, and dashing of the glacier and mountain torrent. The action of the atmosphere is dependent upon the carbonic acid which it contains. This acid is capable of decomposing the silicates of potash and soda, which form part of rocks, seizing the potash and soda and converting the same into carbonates, which are subsequently washed out by water. Besides carbonic acid, chloride of sodium, or common salt, possesses a very powerful solvent action, having in solution the power of dissolv ing the phosphates of the alkaline earths. The tendency of water and atmosphere combined is to level the earth's surface by destroying eminences and filling up hollows. We often find, therefore, in the plains a soil differing widely from its underlying stratum, on account of its being na a mixture of the deposits of streams and the débris of neighboring or more distant mountains. On hills the soil is usually of the same nature as the subsoil. The proportion of organic matter varies exceedingly in different soils. The mixture of various earths and humus, termed loams, constitute the best of soils. These are classified according to the earths which prevail in them, as a sandy loam, etc.; according to their degree of friability, as a free loam, a stiff loam, etc.; or according to both, as a free calcareous loam, etc. They are generally laid on the sides of valleys, along the bases of hills or mountains, or on the banks of upland rivers. In general, much more depends on the texture of a soil, and on its capacity for retaining or parting with water and heat, than on its chemical composition.
What Has Changed in the Last Century
Both accounts describe soil essentially as pulverized rock plus rotted plants: Aiton's in 1910 states flatly that "soil is chiefly crumbled rock," and Collier's in 1921 judges texture more important than chemistry. Modern soil science, following the Russian pedologist V. V. Dokuchaev, instead treats a soil as a natural body with distinct horizons formed over time by parent material, climate, organisms and relief; the USDA's Soil Taxonomy of 1975 sorts the world's soils into a dozen orders, and living organisms are now central rather than incidental, since a single gram of topsoil can hold billions of bacteria (the antibiotic streptomycin was isolated from a soil actinomycete in 1943). Neither entry hints at soil as something that can be lost: the American Dust Bowl of the 1930s produced the Soil Conservation Service in 1935, and erosion and degradation are now treated as a global problem. Soils are also now counted as one of the planet's largest carbon reservoirs, holding more carbon than the atmosphere and vegetation together — a role invisible to both writers.
Written for this edition, 2026.