227. Mineral veins, particularly at their intersections with one another, contain abundant marks of the most violent and repeated disturbance (§ 56.). Not to mention that they owe their first formation to the fracture and displacing of rocks already consolidated, it appears, that they have originated at very different periods, and that the birth of each has been accompanied with convulsions, which shook the foundations of the earth. In Cornwall, for instance, the principal veins, and those which they distinguish particularly by the name of _Lodes_, have nearly the same direction with the strata or vertical schistus, extending from about E. N. E. to W. S. W. These, however, are often intersected nearly at right angles by other mineral veins, called _Cross Courses_, and this hardly ever happens without the latter moving, or, as it is called, heaving the former out of their direction. This plainly indicates, that the cross courses are of later origin than the others, and that their formation was accompanied with such a force, as must, in many substances, have moved the whole body of rock which constitutes the promontory of Cornwall, and probably much more, for several yards, in a horizontal direction. Sometimes, also, both the longitudinal and the cross vein are forced out of their place by a third. These disturbances arise not only from mineral veins, but from veins of porphyry and granite, the production of which has been attended with no less violence than of the others. 228. What is here said of Cornwall, is the history, in some degree, of all mineral countries whatever. The great horizontal _translation_ which has thus accompanied the formation of veins; the movement impressed on such vast bodies of rock, and the frequent renewal of these immense convulsions; are not to be explained by the mild and tranquil dominion of the watery element. They require the utmost power that is known any where to exist, and were it not for the admonitions of the volcano and the earthquake, we might doubt if even subterraneous heat itself possessed an energy adequate to these astonishing effects. 229. From the _heaving_ of one vein by another, it is evident, that there was a force of protrusion in the direction of one of them, that acted at the time of its formation. This force cannot be accounted for on the supposition that veins were produced by the mere shrinking of the strata; for the rocks could not, in that case, have been rent asunder, and impelled forward at the same time. It appears most likely, that fissures in the strata were made, at least in many instances, and the matter poured into them, nearly at the same time, both being effects of the same cause, the expansive force of subterraneous heat.