B A S 



[49] 



B A S 



In scientific language, has a co- 

 lumnar structure, a character also 

 observable in some recent lavas. 

 The columnar arrangement may be 

 more or less observed in all the 

 trappean rocks. Basaltic columns 

 are often curved, they are also 

 frequently articulated. This struc- 

 ture is found, by some highly in- 

 teresting and philosophical experi- 

 ments, to have originated from the 

 manner in which refrigeration took 

 place. Mr. Gregory "Watt melted 

 seven hundred weight of basalt, 

 and kept it in the furnace several 

 days after the fire was reduced. 

 H; fused into a dark-coloured vi- 

 treous mass, with less heat than 

 was required to melt pig-iron ; as 

 refrigeration proceeded, the mass 

 changed into a stony substance, 

 and globules appeared ; these en- 

 larged till they pressed laterally 

 against each other, and became 

 converted into polygonal prisms. 

 The articulated structure and regu- 

 lar forms of basaltic columns have, 

 therefore, resulted from the crys- 

 talline arrangements of the parti- 

 cles in cooling ; and the concavi- 

 ties, or sockets, have been formed 

 by one set of prisms pressing upon 

 others, and occasioning the upper 

 spheres to sink into those beneath. 

 Mantell. 



On . examination with a lens, 

 even the more compact varieties of 

 basalt are seen to be composed of 

 minute crystalline grains. Easalt, 

 in enormous masses, often covers 

 the primary mountain in the Andes, 

 and arranged in regular columns, 

 which to the eye of the traveller 

 appear like immense castles lifted 

 into the sky. Basaltic dykes 

 intersect both primary and second- 

 ary rocks. Few countries in the 

 world present more magnificent 

 basaltic columnar ranges than the 

 north part of Ireland, and some of 

 the Hebrides. The Giant's Cause- 

 way constitutes a small part of a 



vast basaltic range, along the north 

 coast of Ireland, in the county of 

 Antrim. The promontories of 

 Fairhead and Borgue, in the same 

 range, are situated eight miles from 

 each other : these capes consist of 

 various ranges of pillars and hori- 

 zontal strata, which rise from the 

 sea to the height of five hundred 

 feet. Bakewell. 



The ancient inhabitants of Brit- 

 ain formed the heads of their battle 

 axes, which the people called celts, 

 from this stone. These celts re- 

 semble in shape the tomahawks 

 brought from the South Sea Islands. 

 Mr. Powlett Scrope has distin- 

 guished basalt under the following 

 arrangement; 1. Common basalt, 

 composed of felspar, augite, and 

 iron. 2. Leucitic basalt, when 

 leucite replaces the felspar. 3. 

 Olivine basalt, when olivine re- 

 places the felspar. 4. Hauyine 

 basalt, when hauyine replaces the 

 felspar. 5. Ferruginous basalt, 

 when iron is a predominant ingre- 

 dient. 6. Augite basalt, when 

 augite composes nearly the whole 

 rock. 



BASA'LTIC. Composed of basalt ; re- 

 sembling basalt ; containing basalt. 



BASA'LTIFOBM. Kesembling basalt in 

 its columnar form, or structure. 



BASA'LTIC HOENBLENDE. } Two names 



BASA'LTINE. j given to 



the same mineral. A variety of 

 common hornblende to which these 

 names have been given from its 

 having been found commonly in 

 basaltic rocks. The primitive 

 form of its crystals is a rhomboidal 

 prism. It has by analysis been 

 found to consist of silica 58, 

 alumina 27, iron 9, lime 4, and 

 magnesia 1. Its colour i black, 

 dark-green, or yellowish- green. 

 Texture foliated. 



BA'SANITE. (fidffavos, Gr. lapis quo 

 prolatur aurum, la/pis Lydiw.) 

 Lydian stone, a variety of schistose 

 hornstone. This stone acquired 



