by a crack or fissure, varying in width from a mere line to several feet, which is generally filled with broken stone, clay, &c. The strata, a, b, c, &c., must at one time have been continuous; but a fracture having taken place at the fault F, either by the upheaving of the portion A, or the sinking of the portion B, the strata were so displaced that the bed a in B is many feet lower than the same bed a in the portion A.
Fauna. The various kinds of animals peculiar to a country constitute its Fauna, as the various kinds of plants constitute its Flora. The term is derived from the Fauni, or rural deities, in Roman Mythology.
Felspar. A simple mineral, which, next to quartz, constitutes the chief material of rocks. The white angular portions in granite are felspar. This mineral always contains some alkali in its composition. In common felspar the alkali is potash; in another variety, called Albite or Cleavlandite, it is soda. Glassy felspar is a term applied when the crystals have a considerable degree of transparency. Compact felspar is a name of more vague signification. The substance so called appears to contain both potash and soda.
Felspathic. Of or belonging to felspar.
Ferruginous. Any thing containing iron. Etym., ferrum, iron.
Fissile, easily cleft, dividing readily into an indefinite number of parallel laminæ, like slates.
Floetz Rocks. A German term applied to the secondary strata by the geologists of that country, because these rocks were supposed to occur most frequently in flat horizontal beds. Etym., flotz, a layer or stratum.
Flora. The various kinds of trees and plants found in any country constitute the Flora of that country in the language of botanists.
Fluviatile. Belonging to a river. Etym., fluvius, a river.
Foraminifera. A name given by D'Orbigny to a family of microscopic shells. Their different chambers are united by a small perforation or foramen. Recent observation has shown that some at least are not Cephalopoda, as D'Orbigny supposed.