Principles of Geology Part 99

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._, ast??, _mastos_, pap, and ?d??, _odon_, tooth.

MATRIX. If a simple mineral or sh.e.l.l, 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 sh.e.l.ls; 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._, e?a??, _megale_, great, and sa??a, _saura_, lizard.

MEGATHERIUM. A fossil extinct quadruped, resembling a gigantic sloth. _Etym._, e?a, _mega_, great, and ??????, _therion_, wild beast.

MELASTOMA. A genus of MELASTOMACEA, an order of exotic plants of the evergreen tree and shrubby kinds. _Etym._, e?a?, _melas_, black, and st?a, _stoma_, mouth; because the fruit of one of these species stains the lips.

MESOTYPE. A simple mineral, white, and needle-shaped, one of the Zeolite family, frequently met with in the Trap-rocks.

METAMORPHIC ROCKS. A stratified division of hypogene rocks, highly crystalline, such as gneiss and mica-schist, and so named because they have been _altered_ by plutonic action. _Etym._, eta, _meta_, trans, and ??f?, _morphe_, form.

MICA. A simple mineral, having a s.h.i.+ning silvery surface, and capable of being split into very thin elastic leaves or scales. It is often called _talc_ in common life; but mineralogists apply the term talc to a different mineral. The brilliant scales in granite are mica. _Etym._, _mico_, to s.h.i.+ne.

MICA-SLATE, MICA-SCHIST, MICACEOUS SCHISTUS. One of the metamorphic or crystalline stratified rocks of the hypogene cla.s.s, which is characterized by being composed of a large proportion of mica united with quartz.

MIOCENE. A division of tertiary strata intervening between the Eocene and Pliocene formations; so called, because a minority of its fossil sh.e.l.ls are referable to living species. _Etym._, e???, _meion_, less, and ?a????, _kainos_, recent.

MOLa.s.sE. A provincial name for a soft green sandstone, a.s.sociated with marl and conglomerates, belonging to the Miocene Tertiary Period, extensively developed in the lower country of Switzerland.

_Etym._, French, _molle_, soft.

MOLLUSCA, MOLLUSCOUS ANIMALS. Animals, such as sh.e.l.l-fish, which, being devoid of bones, have soft bodies. _Etym._, _mollis_, soft.

MONAD. The smallest of visible animalcules, spoken of by Buffon and his followers as const.i.tuting the elementary molecules of organic beings.

MONITOR. An animal of the saurian or lizard tribe, species of which are found in both the fossil and recent state.

MONOCOTYLEDONOUS. A grand division of the vegetable kingdom (including palms, gra.s.ses, Lilaceae, &c.), founded on the plant having only one _cotyledon_, or seed-lobe. _Etym._, ????, _monos_, single.

MORAINE, a Swiss term for the debris of rocks brought into valleys by glaciers. See p. 228.

MOSCHUS. A quadruped resembling the chamois or mountain goat, from which the perfume musk is obtained.

MOUNTAIN LIMESTONE, OR CARBONIFEROUS LIMESTONE. A series of limestone strata of marine origin, usually forming the lowest member of the Coal Measures.

MOYA. A term applied in South America to mud poured out from volcanoes during eruptions.

MULTILOCULAR. Many-chambered; a term applied to those sh.e.l.ls which, like the nautilus, ammonite, and others, are divided into many compartments. _Etym._, _multus_, many, and _loculus_, a part.i.tion.

MURIATE OF SODA. The scientific name for common culinary salt, because it is composed of muriatic acid and the alkali soda.

MUSACEae. A family of tropical monocotyledonous plants, including the banana and plantains.

MUSCHELKALK. A limestone, belonging to the Upper New Red Sandstone group. Its position is between the Magnesian Limestone and the Lias.

This formation has not yet been found in England, and the German name is adopted by English geologists. The word means sh.e.l.l limestone. _Etym._, _muschel_, sh.e.l.l, and _kalkstein_, limestone.

NAPHTHA. A very thin, volatile, inflammable, and fluid mineral substance, of which there are springs in many countries, particularly in volcanic districts.

NENUPHAR. A yellow water-lily. P. 618.

NEW RED SANDSTONE. A formation so named, because it consists chiefly of sandy and argillaceous strata, the predominant color of which is brick-red, but containing portions which are of a greenish-gray.

These occur often in spots and stripes, so that the series has sometimes been called the variegated sandstone. This formation is divided into the Upper New Red in which the Muschelkalk is included, and the Lower New Red, of which the Magnesian Limestone is a member.

NODULE. A rounded irregular-shaped lump or ma.s.s. _Etym._, diminutive of _nodus_, knot.

NORMAL GROUPS. Groups of certain rocks taken as a rule or standard.

_Etym._, _norma_, rule or pattern.

NUCLEUS. A solid central piece, around which other matter is collected. The word is Latin for kernel.

NUMMULITES. An extinct genus of the order of molluscous animals, called Cephalopoda, of a thin lenticular shape, internally divided into small chambers. _Etym._, _nummus_, Latin for money, and ?????, _lithos_, stone, from its resemblance to a coin.

OBSIDIAN. A volcanic product, or species of lava, very like common green bottle gla.s.s, which is almost black in large ma.s.ses, but semi-transparent in thin fragments. Pumice-stone is obsidian in a frothy state; produced, most probably, by water that was contained in or had access to the melted stone, and converted into steam.

There are very often portions in ma.s.ses of solid obsidian, which are partially converted into pumice.

OCHRE. A yellow powder, a combination of some earth with oxide of iron.

OGYGIAN DELUGE. A great inundation mentioned in fabulous history, supposed to have taken place in the reign of Ogyges in Attica, whose death is fixed in Blair's Chronological Tables in the year 1764 before Christ. See p. 341.

OLD RED SANDSTONE. A formation immediately below the Carboniferous Group. The term Devonian has been recently proposed for strata of this age, because in Devons.h.i.+re they are largely developed, and contain many organic remains.

OLIGOCLASE. A mineral of the felspar family.

OLIVINE. An olive-colored, semi-transparent, simple mineral, very often occurring in the form of grains and of crystals in basalt and lava.

OOLITE, OOLITIC. A limestone; so named because it is composed of rounded particles like the roe or eggs of a fish. The name is also applied to a large group of strata, characterized by peculiar fossils, in which limestone of this texture occurs. _Etym._, ???, _oon_, egg, and ?????, _lithos_, stone.

OPALIZED WOOD. Wood petrified by siliceous earth, and acquiring a structure similar to the simple mineral called opal.