Pebble

Pebble (probably allied to bubble, from the sound of water running among stones), a small, round, water-worn stone of any kind; but with jewellers sometimes an agate—agates being often found as loose pebbles in streams, and those of Scotland in particular being popularly designated Scotch Pebbles. Hence the name has come even to be extended to rock-crystal when not in the crystalline form. Deposits of pebbles (in the sense of water-worn stones) occur among the rocks of all periods, but the pebbles are seldom loose; they are generally cemented together by iron, lime, or silica, forming a pudding-stone of greater or less hardness (see CONGLOMERATE). Single pebbles are sometimes found in deposits which have been formed in perfectly still water, as in chalk and fine silt. They must have been floated to their places entangled in the roots of trees, or attached to the roots of large buoyant seaweeds.—BRAZILIAN PEBBLES (so called from Brazil having been long famous for the purity of its rock-crystal) are very pure pieces of Rock-crystal (q.v.) used by opticians for making the lenses of spectacles, &c.