B A S 



BAT 



also observable in some recent lavas. 

 This structure is found by some highly 

 interesting and philosophical experiments, 

 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 fur- 

 nace several days after the fire was re- 

 duced. It fused into a dark-coloured 

 vitreous mass, with less heat than was 

 required to melt pig-iron ; as refrigera- 

 tion proceeded, the mass changed into a 

 stony substance, and globules appeared ; 

 these enlarged till they pressed laterally 

 against each other, and became converted 

 into polygonal prisms. The articulated 

 structure and regular forms of basaltic 

 columns have, therefore, resulted from 

 the crystalline arrangements of the par- 

 ticles in cooling ; and the concavities, 

 or sockets, have been formed by one set 

 of prisms pressing upon others, and oc- 

 casioning 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. Basalt, 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 

 secondary 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 Causeway 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 situ- 

 ated eight miles from each other : these 

 capes consist of various ranges of pillars 

 and horizontal strata, which rise from the 

 sea to the height of five hundred feet. 

 Bakewell. 



BASA'LTIC. Composed of basalt ; resem- 

 bling basalt ; containing basalt. 



BASA'LTIFORM. Resembling basalt in its 

 columnar form, or structure. 



BASA'LTIC HORNBLENDE. \ Two names 



BASA'LTINE. \ 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 primi- 

 tive 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 is 

 black, dark-green, or yellowish-green. 

 Texture foliated. 



BA'SANITE. (from ftdaavog, Gr. lapis quo 

 probatur aurum, lapis Lydius.) Lydian 



stone, a variety of schistose hornstone. 

 This stone acquired its name from its 

 having been formerly used as a touch- 

 stone in trying the purity of metals : it 

 also was called Lydian stone, from its 

 being found abundantly in Lydia. Ac- 

 cording to an analysis of it, its constituents 

 are, silica 75 per cent., lime, magnesia, 

 carbon, and iron. 



BASILOSAU'RUS. The name of an enormous 

 fossil reptile, described by Dr. Harlan 

 of Philadelphia. Neither the relation of 

 the basilosaurus to other species, nor its 

 geological position, has been accurately 

 determined Mantell. 



BASE, (from basis, Lat.j3a<c. , Gr. base, Fr. 

 basa, It.) 



1. The bottom, or lowest part, of any 

 thing. 



2. In conchology, that part of the shell 

 in univalves by which they are attached 

 to rocks, or other substances : in multi- 

 valves, the opposite extremity to the 

 apex. 



BA'SIN. (bassin, Fr. bacino, It.) In geo- 

 logy, large concavities filled with deposits, 

 as the London basin, the Paris basin, &c. 

 are called basins. The surface of the earth 

 is covered with a series of irregular de- 

 pressions or basins, divided from one 

 another, and sometimes wholly surrounded 

 by projecting portions of subjacent strata, 

 or by unstratified crystalline rocks, which 

 have been raised into hills and mountains 

 of various degrees of height, direction, 

 and continuity. This disposition in the 

 form of basins, which is common to all 

 formations, has been more particularly 

 observed in the carboniferous series, from 

 the beds of coal contained therein having 

 been wrought thi'oughout their whole 

 extent. In consequence of this basin- 

 shaped disposition of the carboniferous 

 strata a most beneficial result obtains, 

 namely, that these strata, which an un- 

 interrupted inclination in one direction 

 only would soon have plunged into depths 

 inaccessible to man's greatest efforts, are, 

 by their being placed around the circumfer- 

 ence of the basin, all brought sufficiently 

 near the surface to be attainable, and are 

 thus made subservient to his benefit and 

 comfort. 



BA'SSET. A term, used by miners, to ex- 

 press an upward slanting direction of a 

 vein, from below to the surface. 



BA'SSETING. Slanting upwards. 



BA'STAKD. (batard, Fr. bastardo, It.) 

 Spurious ; not genuine. 



BATH-STONE. A species of limestone, 

 called also Bath-oolite. This member of 

 the oolite formation has been called 

 the great oolite ; it is of considerable 

 thickness, and yields an abundant supply 

 of freestone for building. It has ob- 



