NOTE XX … CLAY.
Fire and water two great agents; stratification from precipitation; many stratified materials not soluble in water. 1. Stratification of lava from successive accumulation. 2. Stratifications of limestone from the different periods of time in which the shells were deposited. 3. Stratifications of coal, and clay, and sandstone, and iron-ores, not from currents of water, but from the production of morass-beds at different periods of time; morass-beds become ignited; their bitumen and sulphur is sublimed; the clay, lime, and iron remain; whence sand, marle, coal, white clay in valleys, and gravel-beds, and some ochres, and some calcareous depositions owing to alluviation; clay from decomposed granite; from the lava of Vesuvius; from vitreous lavas.