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Show PROSPECTING AND MINING. 561 We dig and blast and assay, and find that here a mineral- bearing ore actually projects from the surface ; and now we are in luck. Are we though ? Well, that depends. There is about one chance in twenty that this little outcrop is the end of a large continuous crev-ice, and about one chance in ten that such a crevice when found will prove a valuable mine. For the reason of this disgusting fact we must go back to the origin of things, and consider how the mountain came to have crevices in it at all. Suppose a mountain of massive rock, or of massive rock below, and capped by sedimentary ( stratified) rock above the whole mass broken across by a force acting from below obviously this would result: the force would split the mount-ain in a tolerably direct course until it neared the surface ; then it would shatter the cap of the mountain, there being less resistance, and the fracturing force would find outlet in a score or a hundred minor crevices. This, if the mountain were all massive rock; but if it were stratified rock, whether limestone, slate, porphyry, or what not, with lines of cleavage already present, the fracturing force would of course follow these lines, and thus you would find scores of crevices at the surface for the one main crevice far below. Indeed, what miners call a " mother lode" is often like a tree in its upward devel-opment : below is the main trunk, above the branches diverge, and sometimes one immense branch strikes off at right angles and reaches the surface hundreds or thousands of feet away. The outcrops which led to the noted Comstock Lode spread over a width of twelve hun-dred feet. From these originate most of the lawsuits as to mining titles ; and if the lucky prospector develops a true vein, or big 60- nanza, he may reasonably expect to find a dozen or more fellows located on the neighboring outcrops, each indulging a hope that the court will decide his to be the true location, or that the owners will buy him off. But this is only one way in which mines are found, though it is the most common way. Sometimes a blind lode is traced by a faint outcrop in a neighboring gulch ; sometimes it is found while running a tunnel for some other purpose or opening another mine ; and oc-casionally a bold outcrop is struck without any indications below it in the way of float. It is the theory of geology that our mountains were once much higher than at present, their tops having been worn away. So, if the crevice extended to the surface of the original mountain as it often did, no doubt it, too, has worn away, and its contents are scattered in the drift. But where such a crevice was filled with hard volcanic rock, the softer rock around it wore away 36 |