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., /uaoroG, mastos, mammilla or little pap, and oduv, 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. 



MEDUSJE. 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., /-teyaXr/, megale, great, 

 and <ravpa, saura, lizard. 



MEGATHERIUM. A fossil extinct quadruped, resembling a gigantic 

 sloth. Etym., ftcya, mega, great, a.nddripioi>,therion, wild-beast. 

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

 evergreen tree, and shrubby exotic kinds. Etym., /^eXae, melas, 

 black, and oro/m, stoma, mouth ; because the fruit of one of the 

 species stains the lips. 



