I am no geologist, and cannot say, especially as I lacked time to examine the place.

At any rate there it was, and there in it appeared the mouth of a great cave that I presume was natural, having once formed a kind of drain through which the lake overflowed when Pongo-land was under water.
We halted, staring dubiously at this darksome hole, which no doubt was the same that Babemba had explored in his youth.

Then the Kalubi gave an order, and some of the soldiers went to huts that were built near the mouth of the cave, where I suppose guardians or attendants lived, though of these we saw nothing.

Presently they returned with a number of lighted torches that were distributed among us.

This done, we plunged, shivering (at least, I shivered), into the gloomy recesses of that great cavern, the Kalubi going before us with half of our escort, and Komba following behind us with the remainder.
The floor of the place was made quite smooth, doubtless by the action of water, as were the walls and roof, so far as we could see them, for it was very wide and lofty.