The aqueous rocks, sometimes called the sedimentary, or fossiliferous, cover a larger part of the earth’s surface than any others. These rocks are stratified, or divided into distinct layers, or strata. The term stratum means simply a bed, or any thing spread out or strewed over a given surface; and we infer that these strata have been generally spread out by the action of water, from what we daily see taking place near the mouths of rivers, or on the land during temporary inundations. For, whenever a running stream charged with mud or sand, has its velocity checked, as when it enters a lake or sea, or overflows a plain, the sediment, previously held in suspension by the motion of the water, sinks, by its own gravity, to the bottom. In this manner layers of mud and sand are thrown down one upon another. [click to continue…]

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The fourth and last great division of rocks are the crystalline strata or schists, called gneiss, mica-schist, clay-slate, chlorite-schist, marble, and the like, the origin of which is more doubtful than that of the other three classes. They contain no pebbles or sand or scoriae, or angular pieces of imbedded stone, and no traces of organic bodies, and they are often as crystalline as granite, yet are divided into beds, corresponding in form to those of sedimentary formations, and are therefore said to be stratified. [click to continue…]

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