The splendid Scotch granite columns, in the vestibule of the Fitzwilliam Museum at Cambridge, are beautiful examples of a modern application of this rock to the arts.”[20] It is also in the Plutonic or igneous rocks that almost all the metals are found; and here we have our first illustration of that order to which we shall frequently call attention; an order as exquisite as can be found in the drawers of a lady’s cabinet, forbidding the thought that anything observable at the present time, in the bowels or on the surface of the crust of the earth, can be attributed to the violent diluvial action of the Noachian deluge. The diagram below represents an ideal section of a mining district. [Illustration: SECTION OF A MINING DISTRICT. ] Here the metalliferous vein, we may suppose, has cropped out on the surface of the ground, or, as the miners say, has “come above grass.” Let us now suppose that the position of this vein of ore, copper, lead, or tin, has been ascertained—that is, how it runs, whether from north to south, or from east to west—and also that the “captains” of the mining district around have given their opinion as to the extent and thickness of this underground vein. The next thing is to obtain this mineral wealth. For this purpose shafts (_a a a a_) must be sunk, which must reach the vein at a certain depth; then will probably follow cross-cuts (_c c c_), called adit levels (technically an “additt”), driven, as may be seen, at the lowest convenient point above the level of the highest water of the valley; and these, in connexion with the shaft, will serve the purpose of draining the mine and carrying the ore above ground. It will also be seen, by reference to the diagram, that the shafts of a mine do not always correspond; sometimes they are sunk vertically to meet the vein, sometimes they are commenced in the very outcrop itself. On this matter the best geological lesson is a visit to Cornwall, where the student will see that everything depends on the locality of a mine, the nature of the slope of the hill, or the character of the rock in which the vein appears, and so on. “The act of sinking a perpendicular shaft downwards to a depth where it is calculated the lode should be cut, may seem to require little further skill than is necessary to determine correctly the spot on the surface where the work is to commence. But the process in this way is exceedingly tedious; and in a mine at work, where many galleries already existing are to be traversed, much greater rapidity is desirable. In such a case the shaft is sunk in several _pieces_ (see diagram below), or, in other words, the sinking is commenced at the same time in different levels; and no small skill is required to lay out the work, so that the different portions of the shaft thus formed may exactly fit when they are joined together. An exceedingly small error of measurement, in any one of these various and