Pebbles, a genus of fossils, comprising 34 species, which are again divided into numerous varieties. They chiefly consist of siliceous earth or flint, being insoluble in water and acids, except the fluoric; while they are destitute of taste, and fusible only by means of alkaline salts, with which they form glass.

Pebbles, in general, are roundish stones, composed of crystalline matter that is debased by various earths of the same kind ; in consequence of which they become clouded, veined, and otherwise variegated. They are usually found at a considerable depth beneath the surface of the earth; and, being intermixed with sands, their strata serve as a natural drain to carry off superfluous waters, and thus prevent the formation of bogs, morasses, etc.

An absurd opinion prevails in some parts of the country, that the swallowing of pebbles is conducive to health; and that such stones assist the stomach in digesting food, This practice probably originated from the example of birds picking up gravel; an expedient which they instinctively adopt, and without which their health becomes impaired. The stomach of man, however, is essentially different in its structure from that of the feathered tribe ; hence such aids are altogether useless, nay hurtful to the comminution of food. —Although many persons may swallow even large pebbles for a series of years, with impunity ; yet this unnatural practice can be productive of no real benefit ; and, as there are cases on record, in which it has proved fatal, the most judicious course will be to avoid so hazardous an experiment.