Page:Geology and Mineralogy considered with reference to Natural Theology, 1837, volume 1.djvu/412

 408 also probable that most of the Springs, that issue from unstratified rocks, are kept in action through the instrumentality of the Faults by which they are intersected.

A similar interruption of continuity in the masses of Primary rocks, and in the rocks of intermediate age between these and the Coal formation, is found to occur extensively in the working of metallic veins. A vein is often cut off suddenly by a Fault, or fracture, crossing it transversely, and its once continuous portions are thrown to a considerable distance from each other. This line of fracture is usually marked by a wall of clay, formed probably by the abrasion of the rocks whose adjacent portions have been thus dislocated. Such faults are known in the mines of Cornwall by the term flucan, and they often produce a similar advantage to those that traverse the Coal measures, in guarding the miner from inundation, by a series of natural dams traversing the rock in various directions, and intercepting all communication between that mass in which he is conducting his operations, and the adjacent masses on the other side of the fluckan or dam.

It may be added also that the Faults in a Coal field, by interrupting the continuity of the beds of coal, and causing their truncated edges to abut against those of the uninflammable strata of shale or grit, afford a preservative against the ravages of accidental Fire beyond the area of that sheet in which it may take its beginning; but for such