lled natural
philosophy and mechanical philosophy. _Etym._, [Greek: physis],
_physis_, nature.

PHYTOLOGY, PHYTOLOGICAL. The department of science which relates to
plants--synonymous with, botany and botanical. _Etym._, [Greek:
phyton], _phyton_, plant, and [Greek: logos], _logos_, discourse.

PHYTOPHAGOUS. Plant-eating. _Etym._, [Greek: phyton], _phyton_,
plant, and [Greek: phagein], _phagein_, to eat.

PISOLITE. A stone possessing a structure like an agglutination of
peas. _Etym._, [Greek: pison], _pison_, pea, and [Greek: lithos],
_lithos_, stone.

PISTIA. P. 618. The plant mentioned by Malte-Brun is probably the
_Pistia Stratiotes_, a floating plant, related to English duckweed,
but very much larger.

PIT COAL. Ordinary coal; called so, because it is obtained by
sinking pits in the ground.

PITCHSTONE. A rock of a uniform texture, belonging to the
unstratified and volcanic classes, which has an unctuous appearance
like indurated pitch.

PLASTIC CLAY. One of the beds of the Eocene Tertiary Period; so
called, because it is used for making pottery. The formation to
which this name is applied is a series of beds chiefly sands, with
which the clay is associated. _Etym._, [Greek: plasso], _plasso_, to
form or fashion.

PLESIOSAURUS. A fossil extinct amphibious animal, resembling the
saurian, or lizard and crocodile tribe. _Etym._, [Greek: plesion],
_plesion_, near to, and [Greek: saura], _saura_, a lizard.

PLIOCENE, OLDER and NEWER. Two divisions of the Tertiary Period
which are the most modern, and of which the largest part of the
fossil shells are of recent species. _Etym._, [Greek: pleion],
_pleion_, more, and [Greek: kainos], _kainos_, recent.

PLUTONIC ACTION. The influence of volcanic heat and other
subterranean causes under pressure.

PLUTONIC ROCKS. Granite, porphyry, and other igneous rocks supposed
to have consolidated from a melted state at a great depth from the
surface.

POLIPARIA. CORALS. A numerous class of invertehrated animals,
belonging to the great division called Radiata.

PORPHYRY. An unstratified or igneous rock. The term is as old as the
time of Pliny, and was applied to a red rock with small, angular,
white bodies diffused through it, which are crystallized felspar,
brought from Egypt. The term is hence applied to every species of
unstratif