ly changed, others are petrified and the organic replaced by mineral matter; some have decayed and left the impression of the bodies, while others have been formed by mineral matter deposited in the cavities left by the decay of the organic body. These last are called casts. The term petrification is applied to those cases, in which organic matter has been replaced by mineral substances. The form and structure of the original body both remain. In casts, the exterior form alone is preserved. Fossils are also called organic remains.

Fosiliferous. Containing organic remains.

Galena. An ore of lead composed of lead and sulphur. Garnet. A simple mineral, which is usually red and crystalized. It is abundant in most primitive rocks.

Gneiss. A stratified primary rock, composed of the same materials as granite, but the mica is distributed in parallel layers, which will give it a striped aspect.

Geode. Geodiferous. Geodes are small cavities in rock, generally lined with quartzose or calcareous crystals.

Geology. A science which has for its object to investigate the structure of the earth, the materials of which it is composed, the manner in which these are arranged, with regard to each other; and it considers the action of all natural causes in producing changes, such as the effects of frost, rain, floods, tides, currents, winds, earthquakes and volcanoes.

Economical Geology refers to the applications of geological facts and observations to the useful purposes of civilized life. Granite. An unstratified rock, composed generally of quartz, feldspar and mica, and it is usually associated with the oldest of the stratified rocks.

Graywacke, Grauwacke. A group of strata in the transition rocks; but the term has been so indefinitely applied, that other names will probably be substituted.

Greenstone. A trap rock composed of hornblende and feld

spar.

Grit. A coarse-grained sandstone.

Gypsum. A mineral, composed of sulphuric acid and lime, and extensively used as a stimulant manure, and for making stucco and plaster casts, &c. It is also called plaster of Paris. Hornblende. A mineral of a dark green or black color, and which is a constituent part of greenstone.

Hornstone. A silicious mineral, approaching to flint in its character.

Hydrography. A science which considers the waters of the globe, principally as relates to navigation, tides, currents, soundings, charts of coasts, &c.

In situ, In place. In their original position where they were formed.

Kidney Ironstone. A variety of ore of iron which receives its name from the somewhat kidney shaped masses in which it occurs. It accompanies the rocks of the carboniferous group.

Laminae. The thin layers into which strata are divided, but to which they are not always parallel.

Lacustrine. Belonging to a lake. Depositions formed in ancient as well as modern lakes, are called lacustrine deposits. Landslip. It is the removal of a portion of land down an inclined surface. It is in consequence of the presence of water beneath, which either washes away the support of the superincumbent mass, or so saturates the material, that they become a slippery paste.

Line of bearing, is the direction of the intersection of the planes of the strata with the plane of the horizon.

Linear survey. A plan of surveying adopted by the United States government, by which the public lands are divided into rectangles by straight lines.

Lignite. Wood naturally carbonized and converted into a kind of coal in the earth.

Littoral. Belonging to the shore.

Loam. A mixture of sand and clay.

Magnetic Meridian. A great circle passing through or by the magnetical poles of the earth; to which the compass needle, if not otherwise hindered, conforms itself. This "line of no variation," is not stationary, but shifts eastward or westward of the true meridian, during a term of years.

Mural Escarpment. A rocky cliff with a face nearly vertitical like a wall.

Mammillary. A surface studded with smooth small segments of spheres like the swell of the breasts.

Mammoth. An extinct species of 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 surfaces covered with conical mammillary

crests.

Matrix. The mineral mass in which a simple mineral is imbedded, is called its matrix or gangue.

Mechanical origin, Rocks of. Rocks composed of sand, pebbles or fragments, are so called, to distinguish them from those of a uniform crystaline texture, which are of chemical origin.

Metamorphic Rocks. Stratified division of primary rocks, such as gneiss, mica slate, hornblende slate, quartz rock, &c.,

and which may probably be regarded as altered sedimentary rocks.

Metalliferous. Containing metals or metallic ores.

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.

Micaceous. In part composed of scales of 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 disposed in layers, so that its flat surfaces give it the appearance of predominating.

Miocene. One of the deposits 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.

Naptha. A fluid, volatile, inflammable mineral, which is common in volcanic districts, and in the vicinity of the salt springs of the United States.

Native Metals. Those portions of metals found in nature in a metallic, or uncombined state, are called native.

New Red Sandstone. "A series of sandy and argillaceous, and often calcareous strata, the prevailing color of which is brick-red, but containing portions which are greenish grey. These occur often in spots and stripes, so that the series has sometimes been called the variegated sandstone. The European, so called, lies in a geological position immediately above the coal measures."

Nodule. A rounded, irregular shaped lump or mass.
Ochre. See bog iron.

Old Red Sandstone. "A stratified rock, belonging to the carboniferous group of Europe."

Oolite, oolitic. "A limestone, 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 fossils."

Organic Remains. See Fossils.

Orthoceratite. The remains of an extinct genus of mollusceous animals, called Cephalopoda. The orthoceratites are long, straight, chambered shells.

Out-crop. See Crop out.

Out-liers. Hills or ranges of rock strata, occurring at some distance from the general mass of the formations to which they

belong. Many of these have been caused by denudation, having removed parts of the strata which once connected with outliers with the main mass of the formation.

Oxyde. A combination of oxygen with another body. The term is usually limited to such combinations as do not present active acid or alkaline properties.

Palaeontology. A science which treats of fossil remains.

Peat. A product resulting from the accumulation of vegetable substances, found in marshy places, in a partially decomposed and sometimes compact state. Peat may be fibrous, ligneous, &c.

Pisolite. A calcareous mineral, composed of rounded concretions like peas.

This

Pliocene. The upper, or more recent tertiary strata. group of strata is divided into the older and newer pliocene rocks.

Petroleum. A liquid mineral pitch. It is common in the region of salt springs in the United States.

Porphyry. A term applied to every species of unstratified rock, in which detached crystals of feldspar are diffused through a compact base or other mineral composition.

Productus. An extinct genus of fossil bivalve sheels.

Plastic Clay. One of the beds of the eocene period. The plastic clay formation is mostly composed of sands with associated beds of clay.

Primary rocks. Those rocks which lie below all the stratified rocks and exhibit no marks of sedimentary origin. They contain no fossils, and are the oldest rocks known. Granite, hornblende, quartz and some slates belong to this division.

· Pudding Stone. See Conglomerate.

Pyrites. A mineral, composed of sulphur and iron. It is usually of a brass yellow, brilliant, often crystalized, and frequently mistaken for gold.

Quartz. A simple mineral, composed of silex. Rock crystal is an example of this mineral.

Rock. All mineral beds, whether of sand, clay or firmly aggregated masses, are called rocks.

Sandstone. A rock composed of aggregated grains of sand. Schist.

Slate.

Seams. "Thin layers which separate strata of greater magnitude."

Secondary Strata. "An extensive series of the stratified rocks, which compose the crust of the globe, with certain characters in common, which distinguish them from another series below them, called primary, and another above them, called tertiary.

Sedimentary rocks. All those which have been formed by

their materials having been thrown down from a state of suspension or solution in water.

Selenite. Crystalized gypsum.

Septaria. Flattened balls of stone, which have been more or less cracked in different directions, and cemented together by mineral matter which fills the fissures.

Serpentine. A rock composed principally of hydrated silicate of magnesia. It is generally an unstratified rock.

Shale.

An indurated clay, which is very fissile.

Shell Marl-Fresh Water Shell Marl. A deposit of fresh water shells, which have disintegrated into a gray or white pulverulent mass.

Shingle. The loose water-worn gravel and pubbles on shores and coast.

Silex. The name of one of the pure earths which is the base of flint quartz, and most sands and sandstones.

Silicious. Containing silex.

Silt. "The more comminuted sand, clay and earth, which is transported by running water.

Simple Minerals-Are composed of a single mineral substance. Rocks are generally aggregates of several simple minerals cemented together.

Slate. A rock dividing into thin layers.

Stalactite. Concreted carbonate of lime, hanging from the roofs of caves, and like icicles in form.

Stalagmites. Crusts and irregular shaped masses of concreted carbonate of lime, formed on the floors of caves, by deposits from the dripping of water.

Stratification. An arrangement of rocks in strata.
Strata. Layers of rock parallel to each other.
Stratum. A layer of rocks; one of the strata.

Strike. The direction in which the edges of strata crop out. It is synonymous with line of bearing.

Syenite and Sienite. A granitic rock, in which hornblende replaces the mica.

Synclinal line and Synclinal axis. When the strata dip downward, in opposite directions, like the sides of a gutter.

Talus. In geology, a sloping heap of broken rocks and stones at the foot of many cliffs.

Tertiary strata. "A series of sedimentary rocks, with characters which distinguish them from two other great series of strata-the secondary and primary-which lie beneath them. Testacea. "Molluscous animals, having a shelly covering." Tepid. Warm.

Thermal.

Hot.

Thin out. Strata which diminish in thickness until they disappear, are said to thin out.