223. It is alleged, in proof of this hypothesis, that mineral veins are found to be less rich as they go farther down, whereas they ought to be richer if they were filled by the projection of melted matter from below. But the fact, that mines are less rich as they descend farther, though it may hold in some instances, is not general, and may therefore be supposed to arise from local causes, such as are, in respect of us, accidental, and beyond the limits to which our theories can be expected to reach. Thus the mines of Mexico and Peru are said to be subject to the preceding rule; but in the mines of Derbyshire and Cornwall, the very contrary is understood to take place. Besides, what we are pleased to call the riches of a mine, are riches relatively to us, and relatively to a distinction which nature does not recognise. The spars and veinstones which are thrown out in the rubbish of our mines, may be as precious in the eyes of nature, as conducive to the great objects of her economy, and are certainly as characteristic of mineral veins, as the ores of silver or gold, to which we attach so great a value. Unless the former are in smaller quantity, or less highly crystallized at great than at small depths, which I believe is not alleged, no conclusion can be drawn from substances, which occupy in general but a small proportion of any vein, and, in their dissemination through it, do not seem to be always guided by the same law. 224. Again, if the veins were filled by deposition from above, we ought to discover in them such horizontal stratification as is the effect of deposition from water, and we should perceive no marks of the materials having been introduced with violence into their place. The Neptunists cannot object to the trial of their theory by these two frets.