392 



Mural Escarpment. A rocky cliff with a face nearly vertical, like a 

 wall. 



MammiJlary. A surface studded with smooth small segments of 

 spheres, like the swell of the breasts. 



Man moth. An extinct species of the elephant. 



Marl. By this term an argillaceous carbonate of lime is usually 

 implied. By custom, its signification is much more extended, and means 

 mineral substances, which act as stimulating or fertilizing manures. 

 There are clay marls, shell marls, and various others. 



Marly clay. Clay containing carbonate of lime. 



Mastodon. A genus of extinct fossil animals allied to the elephant. 

 They are so called from the form of the grinders, which have their sur- 

 faces covered with conical mammillary crests. 



Matrix. The mineral mass in which a simple mineral is imbedded, 

 is called it« matrix or gangue. 



Megatherium. A fossil extinct quadruped, resembling a gigantic 

 sloth. 



Mechanical origin, Rocks of. Rocks composed of sand, pebbles or 

 fragineritft, ari^ ^.^ called, to distinguish them from those of a uuifo.m 

 crysta'line texture, which are of chemical origin. 



Mica. A simple mineral having a shining silvery surface, and capa- 

 ble of being split into very thin elastic leaves or scales. The brilliant 

 scales in granite and gneiss are mica. 



Mica Slate. One of the stratified rocks belonging to the primary 

 class. It is generally fissile, and is characterized by being composed of 

 mica and quartz, of which the former either predominates, or is dis- 

 posed in layers, so that its flat surfaces give it the appearance of pre- 

 dominating. 



Miocene. One o?" the deposits of the tertiary epoch. It is more 

 recent than the eocene, and older than the pliocene. 



M'dlusca. Molluscous animals. "Animals such as shell fish, which, 

 being devoid of bones, have soft bodies." 



Mountain Limestone. "A series of limestone strata, of which the 

 geological position is iinmedi^ti'ly below the coal measures, and with 

 which they also sometimes alternate." 

 Muriite of Soda. Conim )n salt. 

 Naphtha. A flu.d, volaule, inflammable mineral, which is common 



