Precipitate. Substances which, having been dissolved in a fluid, are separated from it by combining chemically and forming a solid, which falls to the bottom of the fluid. This process is the opposite to that of chemical solution.
Producta. An extinct genus of fossil bivalve shells occurring only in the older secondary rocks. It is closely allied to the living genus Terebratula.
Pterodactyl. A flying reptile: species of this genus have been found in the Oolite and Muschelkalk. Some of the finger-joints are lengthened, so as to serve as the expansors of a membranous wing. Hence the name wing-fingered. Etym., πτερον, pteron, a wing, and δακτυλος, dactylos, a finger.
Pubescence. The soft hairy down on insects. Etym., pubesco, the first growth of the beard.
Puddingstone. See "Conglomerate."
Pumice. A light spongy lava, chiefly felspathic, of a white color, produced by gases or watery vapor getting access to the particular kind of glassy lava called obsidian, when in a state of fusion; it may be called the froth of melted volcanic glass. The word comes from the Latin name of the stone, pumex.
Purbeck Limestone, Purbeck Beds. Limestone strata, belonging to the Wealden Group, which intervenes between the Greensand and the Oolite.
Pyrites. (Iron.) A compound of sulphur and iron, found usually in yellow shining-crystals like brass, and in almost every rock, stratified and unstratifled. The shining metallic bodies so often seen in common roofing slate are a familiar example of the mineral. The word is Greek, and comes from πυρ, pyr, fire; because tinder particular circumstances, the stone produces spontaneous heat, and even inflammation.
Pyrometer. An instrument for measuring intense degrees of heat.
Quadrumana. The order of mammiferous animals to which apes belong. Etym., quadrus, a derivative of the Latin word for the number four, and manus, hand, the four feet of those animals being in some degree usable as hands.