_Calcareous sandstones_ usually form a very much better class of soils, partly for the intrinsic reason given above as regards limestones as soil-formers. The calcareous cement is very rarely pure calcite; in most cases it is very impure, as, most commonly, is also the “sand” itself. This is explained from the fact that such rocks (mostly soft and often quite unconsolidated) are, like limestones themselves, the result of deposition in shallow seas or lakes, receiving deposits from the land drainage, and enriched by the animal and vegetable life of such waters. Not uncommonly they contain, disseminated through them, grains of the mineral glauconite (a hydrous silicate of iron and potash), which readily supplies available potash; while the remnants of animals and plants furnish more or less of available phosphates. Thus the general presumption regarding calcareous sandstones is that the derived soils are of good quality, frequently of the very best. The same, however, does not appear to be true of sandstones cemented by dolomite; the soils derived from magnesian sandstones are in many cases noted for their unproductiveness. (See chapt. 3, p. 42). _Ferruginous Sandstones_ manifestly derive no important soil ingredients from their cement when the latter is measurably pure ferric hydrate; and when in addition the sand itself is purely siliceous, the soils resulting from the disintegration of the rocks are very poor. Such are, e.g., the soils derived from the ferruginous sandstones of the Lafayette formation in a part of northern Mississippi and adjacent portions of Tennessee and Alabama, characterized by small scrubby oak or dwarfed pine. On the whole, however, such purely ferruginous quartz sandstones are exceptional, and should not detract from the favorable inferences usually to be drawn from the iron-rust tint of soils (see chapter 15). Sandstones with purely _zeolitic_ cement are on the whole not of frequent occurrence, the zeolites forming, more commonly, the hard portion of a clay-sandstone cement, which disintegrates by their weathering-out. In regions where the tufaceous rocks of eruptives prevail, we not uncommonly find the “volcanic ash” solidly cemented by a zeolitic mass, which is then usually apparent in cavities or crevices in the form of crusts or crystals. Such tuffs are commonly rich in alkalies and lime, but mostly poor in phosphates, and in disintegration form soils of a corresponding nature. They are largely represented in the valleys off Puget Sound, as well as in portions of central Montana, and northward.