Page:Geology and Mineralogy considered with reference to Natural Theology, 1837, volume 1.djvu/416

 412 injected from below, in a state of igneous fusion. A third hypothesis has been recently proposed, which refers the filling of veins to a process of Sublimation from subjacent masses of intensely heated mineral matter, into apertures and fissures of the superincumbent Rocks. A fourth hypothesis considers veins to have been slowly filled by Segregation, or infiltration; sometimes into contemporaneous cracks and cavities, formed during the contraction and consolidation of the originally soft substances of the rocks themselves; and more frequently into fissures produced by the fracture and dislocation of the solid strata. Segregation of this kind may have taken place from electro-chemical agency, continued during long periods of time.