Turrilite. An extinct genus of chambered shells, allied to the Ammonites, having the siphuncle near the dorsal margin.
Unconformable. See "Conformable."
Unoxidized, Unoxidated. Not combined with oxygen.
Veins, Mineral. Cracks in rocks filled up by substances different from the rock, which may either be earthy or metallic. Veins are sometimes many yards wide; and they ramify or branch off into innumerable smaller parts, often as slender as threads, like the veins in an animal, hence their name.
Vertebrated Animals. A great division of the animal kingdom, including all those which are furnished with a back-bone, as the mammalia, birds, reptiles, and fishes. The separate joints of the back-bone are called vertebræ, from the Latin verb verto, to turn.
Vesicle. A small, circular, inclosed space, like a little bladder. Etym., diminutive of vesica, Latin for a bladder.
Vitrification. The conversion of a body into glass by heat.
Volcanic Bombs. Volcanoes throw out sometimes detached masses of melted lava, which, as they fall, assume rounded forms (like bomb-shells), and are often elongated into a pear-shape.
Volcanic Foci. The subterranean centres of action in volcanoes, where the heat is supposed to be in the highest degree of energy.
Wacke. A rock nearly allied to basalt, of which it may be regarded as a soft and earthy variety.