desicco_, to dry up.

DETRITUS. Matter worn or rubbed off from rocks. _Etym._, _de_, from,
and _tero_, to rub.

DICOTYLEDONOUS. A grand division of the vegetable kingdom, founded
on the plant having two _cotyledons_, or seed-lobes. _Etym._,
[Greek: dis], _dis_, double, and [Greek: kotyledon], _cotyledon_.

DIKES. When a mass of the unstratified or igneous rocks, such as
granite, trap, and lava, appears as if injected into a rent in the
stratified rocks, cutting across the strata, it forms a dike. They
are sometimes seen running along the ground, and projecting, like a
wall, from the softer strata on both sides of them having wasted
away; whence they were first called in the north of England and in
Scotland _dikes_, a provincial name for wall. It is not easy to draw
the line between dikes and veins. The former are generally of larger
dimensions, and have their sides parallel for considerable
distances; while veins have generally many ramifications, and these
often thin away into slender threads.

DILUVIUM. Those accumulations of gravel and loose materials, which,
by some geologists, are said to have been produced by the action of
a diluvian wave or deluge sweeping over the surface of the earth.
_Etym._, _diluvium_, deluge.

DIP. When a stratum does not lie horizontally, but is inclined, it
is said to dip towards some point of the compass, and the angle it
makes with the horizon is called the angle of dip or inclination.

DIPTERA. An order of insects, comprising those which have only two
wings. _Etym._, [Greek: dis], _dis_, double, and [Greek: pteron],
_pteron_, wing.

DOLERITE. One of the varieties of the Trap-rocks, composed of augite
and felspar.

DOLOMITE. A crystalline limestone, containing magnesia as a
constituent part. Named after the French geologist Dolomieu.

DUNES. Low hills of blown sand that skirt the shores of Holland,
England, Spain, and other countries.

EARTH'S CRUST. Such superficial parts of our planet as are
accessible to human observation.

EOPYROSIS. A Greek term for a destruction by fire.

ELYTRA. The wing-sheaths, or upper crustaceous membranes, which form
the superior wings in the tribe of beetles. They cover the body, and
protect the true membranous wing. _Etym._, [Greek: elytron],
_elytron_, a sheath.

ENDOGENS. A class of flowering plants, whose