470 GEOLOGY. 



feldspar typically orthoclase; popularly and properly used for any distinctly 

 granular crystalline rock. 



Granitell — a name used to designate a quartz-feldspar rock. 



Granitite — a biotite granite with quartz. 



Granulite — a fine-grained granite with little or no mica. 



Greensand — a sand or sandstone containing a notable percentage of grains of 

 glauconite. 



Greenstone — a comprehensive term used to designate igneous and meta- 

 morphic crystalline rocks of greenish hue and of intricate and often minute crystal- 

 lization; they are mostly dolerites, diabases, and diorites; a convenient term for 

 field use where the constituents cannot be determined, and for general use when 

 the variety is unimportant. 



Greisen — an aggregate of quartz and mica, i.e., a granite without feldspar. 



Greywacke — a sand rock in which the grains are basic silicates instead of 

 quartz. 



Halleflinta — a compact flint-like felsitic rock. 



Hornblendite — a rock essentially composed of hornblende. 



Hornstone — a very compact, silicious rock of horn-like texture, allied to flint; 

 term also applied to flinty forms of felsite. 



Hypogene rocks — those formed deep within the earth under the influence of 

 heat and pressure. 



Ironstone — a rock composed largely of iron, usually applied to clayey rocks 

 having a large iron content. 



Infusorial earth (tripolite) — an earthy or silt deposit consisting chiefly of the 

 silicious shells of diatoms. 



Itacolumite — a flexible sandstone whose pliability is due to an open arrange- 

 ment of sand grains which are held together by scales of mica. 



Jasper — a reddish variety of chalcedonic quartz. 



Keratophyre — a felsite with a large percentage of soda. 



Kersantite — a mica dolerite consisting chiefly of plagioclase, augite, and biotite. 



Lapilli — small fragments of lava ejected from volcanoes; volcanic cinders. 



Laterite — a red, porous, ferruginous residual earth of India and other tropical 

 countries. 



Lava — a molten rock, especially applied to flows upon the surface, whether 

 from vents or from fissures; also applied to the solidified product. 



Lignite (brown coal) — a soft, brown, impure coal. 



Limburgite — a compact basic igneous rock of the basaltic class, composed 

 essentially of augite and olivine, with magnetite iron and apatite as common 

 accessories. 



Limestone — a rock composed primarily of calcium carbonate, though magnesium 

 sometimes replaces a part of the calcium, (See dolomite and marble.) 



Liparite (rhyolite) — an acidic igneous rock of aphanitic or glassy texture, 

 characterized by flowage lines and various microscopic crystals; rhyolite is the 

 more common American name. 



Loess — a very fine porous silicious silt containing some calcareous material 

 which often collects in nodules {Loss Kindchen) or in vertical tubules; charac- 



