GLOSSARY. 
73 
corals distinguished by superficial star-shaped cavities. There 
are several fossil species. 
Magnesian Limestone. An extensive series of beds lying in 
geological position, 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. See 
Table II. K, p. 392. 
Mammillary. A surface which is studded over with rounded pro- 
jections. Etym., mammilla, a little breast or pap. 
Mammiferous. Animals which give suck to their young. Etym., 
mamma, a breast, and fero, to bear. 
Mammoth. An extinct species of the elephant (E. primigenius), of 
which the fossil bones are frequently met with in various coun- 
tries. The name is of Tartar origin, and is used in Siberia for 
animals that burrow underground. 
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 ele- 
phant. So called from the form of the hind teeth or grinders, 
which have their surface covered with conical mammillary crests. 
Etym., fxaarog, mastos, mammilla or little pap, and ocW, 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. When rocks are composed of sand, 
pebbles, or fragments, to distinguish them from those of an 
uniform crystalline texture, which are of chemical origin. 
Medusa. 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., fieyaXtj, megale, great, 
and cravpa, saura, lizard. 
Megatherium. A fossil extinct quadruped, resembling a gigantic 
sloth. Etym., [xeya, mega, great, and B-qpiov, therion, wild-beast. 
Melastoma. A genus of Melastomacea, an order of plants of the 
evergreen tree, and shrubby exotic kinds. Etym., pzkctQ, melas, 
black, and arofia, stoma, mouth ; because the fruit of one of the 
species stains the lips. 
