82 GEOLOGY 



Aphanite. A rock whose constituents are so minute as to be indistin- 

 guishable to the naked eye; rather a condition of various rocks than the 

 name of any specific rock. 



Arenaceous rocks. Either those which are mainly sand, or those in which 

 sand is a notable accessory. 



Argillite. A clayey rock; usually applied to hard varieties only. 



Arkose. A sand or sandstone formed of disaggregated granite or similar 

 rock in which a notable part of the grains are feldspar or other silicate; sand 

 when undefined, is understood to be quartzose. 



Augitite. A rock made up mainly of augite. 



Basalt. A dark, compact basic igneous rock consisting of a mass of 

 minute crystals sometimes with more or less glassy base, often containing 

 also visible crystals; composed of plagioclase and pyroxene, with olivine 

 magnetite, or titaniferous iron as common accessories; a basic lava in which 

 the crystallization has taken place rapidly; usually rich in crystallites or 

 microlites; graduates into dolerite aud basic andesite. 



Bituminous coal. Common soft coal, intermediate between lignite and 

 anthracite; contains much bituminous matter, i. e., hydrocarbons. 



Bowlders. Rounded masses of rock, such as those that have been shaped 

 by glaciers. 



Breccia. A rock composed of angular fragments, contrasted with pud- 

 ding-stone or conglomerate, in which the fragments are rounded. 



Buhrstone. A compact, flint-like silicious rock full of small cavities, so 

 named from use as millstones. 



Calc-sinter (calcareous tufa) . A loose cellular deposit of calcium carbonate 

 made by springs; travertine is the better term, as tufa should be left for 

 volcanic elastics. 



Cannel coal. A very fine-grained homogeneous bituminous coal, giving 

 off much gas and burning with a candle-like flame. 



Chalk. A fine-grained soft rock composed essentially of calcium car- 

 bonate derived from minute marine organisms. 



Chlorite schist. A schistose rock in which chlorite is a predominant 

 mineral; usually greenish, whence the name. 



Clastic rock. Formed from the debris of broken-down rocks; the same 

 as fragmental or detrital rock. 



Clay. A term commonly applied to any soft, unctuous, adhesive deposit, 

 but in strict use confined to material composed of aluminum silicate; many 

 so-called clays are chiefly silicious silts or loams. 



Clay ironstone. A clayey rock heavily charged with iron oxide, usually 

 limonite; commonly in concretionary form. 



Clinkstone. A name applied to phonolite because of its metallic clinking 

 sound when struck; composed of orthoclase, with nephelite and one or more 

 of the ferromagnesian minerals as accessories. 



