Fissures.—Seams or crevices in rocks formed by volcanic or earthquake action, and when filled subsequently by metal or metallic ores they become fissure veins.
Fog.—Watery vapor condensed in the lower part of the atmosphere and disturbing its transparency. It differs from cloud only in being near the ground, and from mist in not approaching so nearly to fine rain.
Geography (je-ŏg´rȧ-fy̆).—The science which treats of the world and its inhabitants; a description of the earth, or a portion of the earth, including its structure, features, products, political divisions, and the people by whom it is inhabited.
Astronomical, or Mathematical Geography treats of the earth as a planet, of its shape, its size, its lines of latitude and longitude, its zones and the phenomena due to the earth’s diurnal and annual motions.
Physical Geography or Physiography treats of the conformation of the earth’s surface, of the distribution of land and water, of minerals, plants, animals, etc., and applies the principles of physics to the explanation of the diversities of climate, productions, etc.
Political Geography treats of the different countries into which the earth is divided with regard to political and social institutions and conditions.
Geology (jē-ŏl´o-jy̆).—The science which treats: (a) Of the structure and mineral constitution of the globe; structural geology. (b) Of its history as regards rocks, minerals, rivers, valleys, mountains, climates, life, etc.; historical geology. (c) Of the causes and methods by which its structure, features, changes, and conditions have been produced; dynamical geology.
Goniatites (gō-ni-a-tī´tēz).—Fossil remains of Ammonites, many species of which are found in Devonian and Carboniferous Limestone.
Hail (hāl).—Frozen rain, or particles of ice precipitated from the clouds, where they are formed by the congelation of vapor. The separate particles are called hailstones.
Harmattan (här-măt´tan).—A dry, hot wind, prevailing on the Atlantic coast of Africa, in December, January, and February, blowing from the interior or Sahara. It is usually accompanied by a haze which obscures the sun.