Basalt

(busaull.) [L. basal tes.] (Geol. and Min.) A heavy,stony rock of igneous origin, composed of feldspar, augite, and iron intimately mixed,with other minerals imbedded,the commonest of which is Olivine. It is usually ofa black Fig. 63.-BASALTIC COLUMNS. or bluish color. (Coast of Illawana, New South Wales.) It is confined to no geological age and to no country. It is found in sheets of more or le thickne , and of variable width. It is frequently found split vertically (Fig. 63) into angular columns, which vary from the utmost degree of rudene to columns of a very regular structure, such as are seen at the Giant's Causeway and at Staff a. It is sometimes of volcanic origin, but more often the interjected rock of a dike, and its tendency to split at right angles to the cooling surfaces is then clearly shown. [s. 76] IMG:p0105_0.jpg:Gravür