Geology, Geognosy. Both mean the same thing; but with an unnecessary degree of refinement in terms, it has been proposed to call our description of the structure of the earth geognosy (Etym., γεα, gea, earth, and γινωσcω, ginosco, to know), and our theoretical speculations as to its formation geology (Etym., γεα, and λογος, logos, a discourse).
Glacier. Vast accumulations of ice and hardened snow in the Alps and other lofty mountains. Etym., glace, French for ice.
Glacis. A term borrowed from the language of fortification, where it means an easy insensible slope or declivity, less steep than a talus, which see.
Gneiss. A stratified primary rock, composed of the same materials as granite, but having usually a larger proportion of mica and a laminated texture. The word is a German miner's term.
Gramineæ. The order of plants to which grasses belong. Etym., gramen, grass.
Granite. An unstratified or igneous rock, generally found inferior to or associated with the oldest of the stratified rocks, and sometimes penetrating them in the form of dikes and veins. It is usually composed of three simple minerals, felspar, quartz, and mica, and derives its name from having a coarse granular structure; granum, Latin for grain. Waterloo bridge, and the paving-stones in the carriage-way of the London streets, afford good examples of the most common varieties of granite.
Greensand. Beds of sand, sandstone, limestone, belonging to the Cretaceous Period. The name is given to these beds because they often, but not always, contain an abundance of green earth or chlorite scattered through the substance of the sandstone, limestone, &c.
Greenstone. A variety of trap, composed of hornblende and felspar.
Greywacké. Grauwacke, a German name, generally adopted by geologists for some of the most ancient fossiliferous strata. The rock is very often of a gray color; hence the name, grau, being German for gray, and wacke, being a provincial miner's term.
Grit. A provincial name for a coarse-grained sandstone.