The incrusting concretionary limestone

differs little from the preceding except in the rapidity of its formation, and in being moulded upon some body whose shape it a umes. These deposits from calcareous springs, form equally on vegetable bodies, on stones, metals, within pipes of cast iron, wood, or lead. The incrustations on vegetable and animal substances are vulgarly called petrifactions, as the organic fibres are replaced by stone. One of the most curious springs of this nature is at the baths of Saint Philip, in Tuscany, where the water flows in almost a boiling state, over an enormous ma of alabaster which it has produced. The carbonate of lime seems to be held in solution here by sulphuretted hydrogen, which flies off when the water i ues to the day. Dr. Vegny has taken advantage of this property of the spring, to obtain ba o-relievo figures of great whitene and solidity. He makes use of sulphur moulds.