ensive series of beds, the geological
position of which is immediately above the Coal Measures; so called,
because the limestone, the principal member of the series, contains
much of the earth magnesia as a constituent part.

MAMMIFEROUS. Mammifers. Animals which give suck to their young. To
this class all the warm-blooded quadrupeds, and the Cetacea, or
whales, belong. _Etym._, _mamma_, a breast, _fero_, to bear.

MAMMILLARY. A surface which is studded over with rounded
projections. _Etym._, _mammilla_, a little breast or pap.

MAMMOTH. An extinct species of the elephant (_E. primigenius_), of
which the fossil bones are frequently met with in various countries.
The name is of Tartar origin, and is used in Siberia for animals
that burrow under ground.

MANATI. One of the Cetacea, the sea-cow, or lamantine (_Trichechus
manatus_, Lin.)

MARL. A mixture of clay and lime; usually soft, but sometimes hard,
in which case it is called indurated marl.

MARSUPIAL ANIMALS. A tribe of quadrupeds having a sack or pouch
under the belly, in which they carry their young. The kangaroo is a
well-known example. _Etym._, _marsupium_, a purse.

MASTODON. A genus of fossil extinct quadrupeds allied to the
elephants; so called from the form of the hind teeth or grinders,
which have their surface covered with conical mammillary crests.
_Etym._, [Greek: mastos], _mastos_, pap, and [Greek: odon], _odon_,
tooth.

MATRIX. If a simple mineral or shell, in place of being detached, be
still fixed in a portion of rock, it is said to be in its matrix.
_Matrix_, womb.

MECHANICAL ORIGIN, ROCKS OF. Rocks composed of sand, pebbles, or
fragments, are so called to distinguish them from those of a uniform
crystalline texture, which are of chemical origin.

MEDUSAE. A genus of marine radiated animals, without shells; so
called, because their organs of motion spread out like the snaky
hair of the fabulous Medusa.

MEGALOSAURUS. A fossil gigantic amphibious animal of the saurian or
lizard and crocodile tribe. _Etym._, [Greek: megale], _megale_,
great, and [Greek: saura], _saura_, lizard.

MEGATHERIUM. A fossil extinct quadruped, resembling a gigantic
sloth. _Etym._, [Greek: mega], _mega_, great, and [Greek: therion],
_therion_, wild beast.

MELASTOMA. A genus of MELASTOMACEA, an order of exotic plants of the