This is an immense rampart or gallery of grisly black scoria and lava, about half a mile wide, running all round the pit, slightly sloping inward, and not unfrequently overflowed in eruptions. By it you learn the dimensions of the great lake to which this is now the shore. It may be compared to the wide beach of an ocean, seldom flooded all over except in very high tides; or to a great field of thick shore ice, from under which the tide has retired, leaving it cracked and rent, but not so as to break up the general evenness of its surface. The upper crust is generally glossy, cellular, and cinder-like, brittle and crackling under the feet; but directly underneath the superficies, hard and compact, as proved by inspecting the great seams and fissures, from some of which flickering currents of hot air, and from others scalding steam and smoke are continually issuing. Pound on it, and you will hear deep, hollow reverberations, and sometimes your pole will break through a place like the rotten trap-door of some old ruin, and open upon you a hideous black hole without bottom. Over this great volcanic mole or offset, we proceeded to make our way toward the caldron in the southeast, pounding before us with our pole, like men crossing a river to find whether the ice ahead will bear them. We stopped every now and then to examine and get up on to some great cone or oven, which had been formed after the congelation of the crust, by pent up gas blowing out from beneath the cooling lava, raising it as in great bubbles, and letting its black, viscous vomit dribble from the top, and flow down sluggishly and congeal before it had found a level, like ice in very cold weather over a waterfall. Thus it would flow over the Black Ledge, hardening sometimes in round streams like a cable, or in serpentine forms like a great anaconda; and again it would spread out from the foot of the cone a little way, in forms like a bronze lion's foot. The surface was frequently broken, or ready to break, with the weight of one's body, from the fiery liquid having subsided after the petrifaction of the crust. Generally, too, the hardened lava seemed to have been flowed over, like ice near the shore when the tide rises and goes down, with a thin scum of lava that became shelly and crepitated under the foot like shelly ice. Then, as we went further into the bed of the crater, gradually going down, we would come to places where, like as in frozen mill-ponds, whence the water has been drawn off, the congealed lava had broken in to the depth sometimes of fifty and one hundred feet. Every where, too, there were great fissures and cracks, as in fields of river ice, now and then a large air-hole, and here and there great bulges and breaks, and places from which a thin flame would be curling, or over which you would see a glimmer like that which trembles over a body of fresh coals or a recently-burned lime-kiln. Touch your stick there, and it would immediately kindle.