Porphyry. Any rock having crystals imbedded in a base of other mineral composition. Thus granite is a porphyritic rock, having crystals of feldspar and mica imbedded in a quartz base.
Predaceus. Preying upon other animals.
Prehnite. A mineral.
Primary, or Primitive. This name is commonly applied to the rocks which underlie those that are manifestly of mechanical origin and contain fossils.
Prodectus. A bivalve shell.
Pterichthys. (Winged fish.) A fossil of the Old red sandstone.
Pterodactyl. A remarkable genus of reptiles adapted for flight; its remains have been found in a fossil state throughout the Secondary rocks.
Pteropoda. Marine animals having wing-like fins.
Pudding stone. The name often given to coarse conglomerates in which the fragments or pebbles are rounded.
Pyrites. A name given to the combinations of certain metals with sulphur.