Chapter IV

THE VARIOUS ROCKS AS SOIL-FORMERS, 47.—General Classification,
47.—Sedimentary, Metamorphic, Eruptive, 47.—Sedimentary
Rocks; Limestones, Sandstones, Clays, Claystones, Shales,
47.—Metamorphic Rocks: Formed from Sedimentary, 48.—Igneous
or Eruptive Rocks, Basic and Acidic, 49.—_Generalities
Regarding Soils Derived from Various Rocks_, 49.—Variations
in Rocks themselves. Accessory Minerals, 50.—Granites;
not always True to Name; Sierra Granites, 51.—Gneiss.
Mica-schist, 51.—Diorites, 51.—Diabases, 51.—Eruptive
Rocks; Glassy ones Weather Slowly; Basaltic Oxidize
Rapidly, 52.—Red Soils of Hawaii, Pacific Northwest,
52.—Trachyte Soils; Light-colored, rich in Potash.
Rhyolites generally make Poor Soils, 53.—_Sedimentary
Rocks_, 53.—Limestones, 53.—“A Limestone Country is a
Rich Country,” 53.—Residual Limestone Soils; from “Rotten
Limestone” of Mississippi; Table, 54.—Shrinkage of Surface,
55.—Sandstone Soils, 55.—Vary According to Cement, and
Nature of Sand, 55.—Calcareous, Dolomitic, Ferruginous,
Zeolitic, 56.—Clay-sandstones, Claystones, 57.—_Natural
Clays_, 57.—Great Variety, Enumeration and Definition,
58.—Colors of Clays, 58.—_Colloidal Clay_, Nature and
Properties, 59.—Plasticity; Kaolinite Non-plastic,
59.—Causes of Plasticity, 60.—Separation of Colloidal Clay,
its Properties, 61.—Effects of Alkali Carbonates on Clay,
62.