GLOSSARY. 
Mastodon. A genus of extinct fossil animals allied to the 
elephant. They are so called from the form of the grinders, 
which have their surfaces covered with conical mammillary 
crests. 
Matrix. The mineral mass in which a simple mineral is im- 
bedded is called its matrix or gangue. 
Megatherium. A fossil extinct ; a quadruped resembling a gi- 
gantic sloth. 
Mechanical origin, Rocks of. — Rocks composed of sand, peb- 
bles, or fragments, are so called, to distinguish them from those 
of a uniform crystalline texture, which are of chemical origin. 
Mica. A simple mineral, having a shining silvery surface, and 
capable 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 pri- 
mary class. It is generally fissile, and is characterized by be- 
ing composed of mica and quartz, of which the former either pre- 
dominates, or is disposed in layers, so that its flat surfaces give 
it the appearance of predominating. 
Miocene. One of the deposites of the tertiary epoch. It is 
more recent than the eocene, and older than the pliocene. 
Mollusca. 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 immediately below the coal measures, 
and with which they also sometimes alternate." 
Muriate of Soda, Common salt. 
N. 
Naptha. A fluid volatile inflammable mineral, which is com- 
mon in volcanic districts, and in the vicinity of the Salt Springs 
of the United States. 
New Red Sandstone. " A series of sandy and argillaceous, 
and often calcareous strata, the prevailing colour of which is 
brick red, but containing portions which are greenish gray. 
These occur often in spots and stripes, so that the series has 
sometimes been called the variegated sandstone. The Euro- 
pean, so called, lies in a geological position immediately above 
the coal measures." 
Nodule. A rounded, irregular shaped lump or mass. # 
O. 
Old Red Sandstone. " A stratified rock belonging to the car- 
boniferous group of Europe." 
Oolite. " A hmestone, so named, because it is composed of 
rounded particles like the roe or eggs of fish. The name is also 
applied to a large group of strata characterized by peculiar fos- 
sils." 
