Page:Geology and Mineralogy considered with reference to Natural Theology, 1837, volume 1.djvu/409

 Rh qualities, and variously adapted to the habitation of Man, and the inferior tribes of terrestrial animals.

In our last Chapter we considered the advantages of the disposition of the Carboniferous strata in the form of Basins. It remains to examine the further advantages that arise from other disturbances of these strata by Faults or Fractures, which are of great importance in facilitating the operations of Coal mines; and to extend our inquiry into the more general effect of similar Dislocations of other strata, in producing convenient receptacles for many valuable Metallic ores, and in regulating the supplies of Water from the interior of the earth, through the-medium of Springs.

I have elsewhere observed that the occurrence of Faults, and the Inclined position in which the strata composing the Coal measures are usually laid out, are facts of the highest importance, as connected with the accessibility of their mineral contents. From their inclined position, the thin strata of Coal are worked with greater facility than if they had been horizontal; but as this inclination has a tendency to plunge their lower extremities to a depth that would be inaccessible, a series of Faults, or Traps, is interposed, by which the component portions of the same formation are arranged in a series of successive tables, or stages, rising one behind another, and elevated continually upwards towards the surface, from their lowest points of depression. (See Pl. 65. Fig. 3. and Pl. 66. Fig. 2.) A similar effect is often produced, by Undulations or contortions of the strata, which give the united advantage of inclined position and of keeping them near the surface. The Basin-shaped structure which so frequently occurs in coal fields, has a tendency to produce the same beneficial consequences. (See Pl. 65. Figs. 1. 2. 3.)

But a still more important benefit results from the occurrence of Faults or Fractures, without which the contents of