Every artificial excavation-every well and cellar-every cut for a fort, common road, railway, or canal-every quarry-every tunnel through a mountain-and every pit and gallery of a mine bored into the solid earth, furnish means of investigating its interior. Still more do the inland precipices, and the rocky promontories and headlands along the rivers, lakes, seas, and oceans; the naked mountain-sides ribbed with strata, that bound the defiles, gorges, and valleys; the ruins accumulated at the feet of lofty pinnacles and barriers, and those that have been transported and scattered, far and wide, over the earth; present us with striking features of the internal structure of our planet. Most of all, do the inclined strata push up their hard edges, in varied succession, and thus faithfully disclose the form and substance of the deep interior, as it exists many miles and leagues beneath the observer's feet.