uently included in the mass of the Trap-rocks.

STRATIFIED. Rocks arranged in the form of _strata_, which see.

STRATIFICATION. An arrangement of rocks in _strata_, which see.

STRATA, STRATUM. The term stratum, derived from the Latin verb
_struo_, to strew or lay out, means a bed or mass of matter spread
out over a certain surface by the action of water, or in some cases
by wind. The deposition of successive layers of sand and gravel in
the bed of a river, or in a canal, affords a perfect illustration
both of the form and origin of stratification. A large portion of
the masses constituting the earth's crust are thus stratified, the
successive strata of a given rock preserving a general parallelism
to each other; but the planes of stratification not being perfectly
parallel throughout a great extent like the planes of _cleavage_,
which see.

STRIKE. The direction or line of bearing of strata, which is always
at right angles to their prevailing dip.

STUFAS. Jets of steam issuing from fissures in volcanic regions at a
temperature often above the boiling point.

SUBAPENNINES. Low hills which skirt or lie at the foot of the great
chain of the Apennines in Italy. The term. Subapennine is applied
geologically to a series of strata of the Older Pliocene Period.

SYENITE. A kind of granite; so called, because it was brought from
Syene in Egypt.

TALUS. When fragments are broken off by the action of the weather
from the face of a steep rock, as they accumulate at its foot, they
form a sloping heap, called a talus. The term is borrowed from the
language of fortification, where _talus_ means the outside of a wall
of which the thickness is diminished by degrees, as it rises in
height, to make it the firmer.

TARSI. The feet in insects, which are articulated, and formed of
five or a less number of joints.

TERTIARY STRATA. A series of sedimentary rocks, with characters
which distinguish them from two other great series of strata--the
secondary and primary--which lie _beneath_ them.

TESTACEA. Molluscous animals, having a shelly covering. _Etym._,
_testa_, a shell, such as snails, whelks, oysters, &c.

THALLOGENS. A class of flowerless plants including all those that
have no defined axis, stem, or leaves; as Lichens, Seaweeds, and
Fungi. _Etym._, [Greek: thallos], _thallos_, a branch, and [Gr