424 Adventures in Scenery 



magnesium, usually with iron. Color ranges between black and white, 

 through green, dark brown, yellow, pink, and rose-red. 



Igneous (From ignis, meaning fire). Formed by solidification from a 

 molten state. One of the two great classes into which all rocks are 

 divided. Contrasted with sedimentary. Also called plutonic; includes 

 volcanic rocks. 



Joint A crack or fissure, one of an approximately parallel set of fissures, 

 from a few inches to many feet apart. 



Latite A broad family name including the effusive (extrusive) monzonites. 

 Plagioclase and orthoclase (feldspars) both present, with ferromagnesian 

 minerals in varying amounts. Texture may be glassy, felsitic, or 

 porphyritic. 



Lava A general name for the molten outpourings of volcanoes. Fluid rock, 

 as that which issues from a volcano or a fissure in the earth's crust; also 

 the same material solidified by cooling. Commonly regarded as molten 

 rock, but more exactly it is mineral matter dissolved in mineral matter, 

 the solution taking place only at high temperatures. 



Limestone The general name for sedimentary rocks composed essentially of 

 calcium carbonate. 



Loam A term applied to soils. A mixture of clay and sand. Varies toward 

 clay loam on one hand and sandy loam on the other. 



Lode A fissure in the country rock filled with mineral; usually applied to 

 metalliferous veins or lodes. 



Magma Liquid molten rock; the molten material from which igneous rocks 

 are formed by solidification. 



Massive Homogeneous, without stratification. In mineralogy, without defi- 

 nite crystalline structure. 



Metamorphism Change in the texture or composition of a rock, produced 

 (principally) by heat, moisture, and pressure, involved in earth deforma- 

 tion. 



Mica A hydrous silicate having a very fine basal cleavage that renders it 

 capable of being split into thin, tough, transparent plates. The common 

 varieties are muscovite (silicate of potash), and biotite (silicate of mag- 

 nesium and iron). 



Mineral Inorganic material having a definite chemical composition. 



Monadnock A rock, hill, or plateau standing above a peneplain, not yet 

 worn away by erosion. 



Monzonite Feldspars, with biotite (mica) and horneblende. 



Moraine A French term meaning "a heap of stones." An accumulation of 

 earth materials, as stones, clay, etc., carried and finally deposited by a 

 glacier. 



