Such an eternal conflagration must have an outlet for the vast quantity of vapor generated, and Ashman wondered that he had not noticed the ascending smoke on his way thither.  He recalled that when he and his friend were coming up the Xingu, far below the last rapids, they observed a dark cloud resting in the western horizon.  There was no thought at that time that it was caused by a burning mountain, but such must have been the fact.  The most singular fact was, that while on his way across the lake to the tunnel, he had failed to notice and remark it.

There was a steady draft in the direction of the flaming cavern.  He had observed it while paddling through the tunnel where it was strong enough to assist in the propulsion of the canoe.  It was caused by the ascent of the vapor through the chimney of the fiery mountain, and averted the intolerable heat that otherwise would have been felt over every portion of the lake.  As it was, a moderate increase of temperature was perceptible.

Ashman was tempted to paddle the canoe to the black rocks which separated the chasm from the lake, and he timidly moved the blade, restrained by the fear of something in the nature of a “back draft,” which might consume them before they could escape.

Ariel assured him that she had never encountered or heard of anything of the kind, though she had often visited this remarkable region in the company of her father.  Thereupon Ashman sent the boat ahead faster than before, and a minute later the bow touched the rocky wharf.

Stepping out, he drew the bow upon the rocks, so as to hold it fast, and, extending his hand, assisted her to shore.  Then he drew the craft still further up, and, taking her hand again in his own, began picking their way over the jagged bowlders and stones to the edge of the volcano.

From the margin of the lake to the other side of the mass of rocks was a hundred feet.  This may be defined as a solid wall, shutting out the water from the burning mountain.  The rocks rose to a height of a dozen rods or so, attaining which a spectator found himself half-way across the dividing ridge, where, viewed from the lake, his figure looked as if stamped in ink on the crimson background.

It was here that the lovers paused and viewed the striking picture spread out before their vision.

That which they saw might properly be considered the crater of the volcano.  It was four or five acres in extent, irregular in contour, and so filled with gases and vapors that one could not see the bottom, while the jagged boundary on the farther side came out to view only at intervals, when the obstructing smoke was swept aside.

Spiral columns of black vapor twisted swiftly upward from the fiery depths, sometimes side by side, and sometimes they would unite and climb toward the opening above, like a couple of huge serpents struggling together.  The air quivered and pulsated in certain portions, as if with fervid heat, and Ashman fancied once or twice that he caught glimpses of a vast mass of molten stuff, far down in the mountain, surging; seething and turning upon itself with terrific violence.  But the glare was so dazzling that it was like staring at the sun, and he was compelled to withdraw his gaze.