The tunnel through which Ashman propelled the canoe containing himself and Ariel, was more than a hundred yards in length. It was only for the smallest distance that the craft was in darkness, when the water began to reflect light and reveal its outlines.

A few minutes later the tunnel was passed, and they debouched into an expansion of the enchanted lake. The second division was similar to the other and almost as large, but its appearance was tenfold more wonderful.

The sheet of water may be said to have been divided into two nearly equal parts by the narrow tunnel running under the mass of rocks described. One division was in the outer air, after the usual fashion of lakes, while the other was wholly underground.

The interior lake was nearly circular in shape, with an arching roof hundreds of feet high. It was surrounded by towering crags, and volcanic masses of stone, which gave it an appearance different from anything on which Fred Ashman had ever looked. Nothing grander, wilder, more picturesque or romantic can be conceived. It was a scene which an explorer could stand for hours and contemplate in rapt admiration.

But the most amazing feature of this underground lake was the way in which it was illuminated, so that every portion stood out in as bold relief as if under the flaming sun of mid-day.

At the western side, the shore, as was the case in nearly all other directions, was a mass of jagged rocks, piled upon each other in the wildest confusion. Beyond these rocks, was a vast chasm above the level of the lake, and extending right and left for a distance of fifty rods. This huge chasm was one mass of crimson light, whose rays pierced every nook and cranny on every side of the lake.

The eye gazing in that direction saw something similar to that which greets the traveller in the far north, when viewing the play of the aurora borealis in the horizon, or when the red sun is rising from its ocean bed.

This enormous opening was so surcharged with light that Ashman, after contemplating it but a minute or two, did not need to ask its source. Beyond the area of illumination was the burning mountain whose blood-red glow covered the entire surface and shores of the underground portion of the enchanted lake. The volcano had been aflame for ages, and was likely to continue to burn for centuries to come.

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 e............