The “St. Louis Republic” says a curiosity will be presented at the World's Fair, in New York, that will surprise most mineralogists, and the learned and curious in these matters. It is from the pilot knob. On the summit of the Knob, which bears evidence ot having been, at one time, subject to volcanic action, and where immense sheets of iron have been thrown out, of various thickness, length, and breadth—many standing in the very position and inclination that the last throe ot the internal furnace poured them out—there is one of immense width, length, and breadth, but nearly of uniform thickness. A portion of this slab, several feet in length and breadth, has been detached, and will be sent to the World's Fair. It will be by far the largest sample ore of such purity, that has sver been seen by those who have not visited the Knob and Iron Mountain, and yet will be but an imperfect representation of the ores there. Some very important and extraordinary developments have been made in the [ace of the Shepherd Mountain. This mountain faces the Knob, separated only by a small valley. In prosecuting, a vein has been discovered, and there are doubtless hundreds of others, more extraordinary than anything yet supposed to exist in that region.