an old, semi-tropical swamp.  To make matters worse, the place seemed to be a favorite breeding-place of the Jaracaca snake, the most venomous and aggressive in South America.  Again and again these horrible creatures came writhing and springing towards us across the surface of this putrid bog, and it was only by keeping our shot-guns for ever ready that we could feel safe from them.  One funnel-shaped depression in the morass, of a livid green in color from some lichen which festered in it, will always remain as a nightmare memory in my mind.  It seems to have been a special nest of these vermins, and the slopes were alive with them, all writhing in our direction, for it is a peculiarity of the Jaracaca that he will always attack man at first sight.  There were too many for us to shoot, so we fairly took to our heels and ran until we were exhausted.  I shall always remember as we looked back how far behind we could see the heads and necks of our horrible pursuers rising and falling amid the reeds.  Jaracaca Swamp we named it in the map which we are constructing.

The cliffs upon the farther side had lost their ruddy tint, being chocolate-brown in color; the vegetation was more scattered along the top of them, and they had sunk to three or four hundred feet in height, but in no place did we find any point where they could be ascended.  If anything, they were more impossible than at the first point where we had met them.  Their absolute steepness is indicated in the photograph which I took over the stony desert.

“Surely,” said I, as we discussed the situation, “the rain must find its way down somehow.  There are bound to be water-channels in the rocks.”

“Our young friend has glimpses of lucidity,” said Professor Challenger, patting me upon the shoulder.

“The rain must go somewhere,” I repeated.

“He keeps a firm grip upon actuality.  The only drawback is that we have conclusively proved by ocular demonstration that there are no water channels down the rocks.”

“Where, then, does it go?” I persisted.

“I think it may be fairly assumed that if it does not come outwards it must run inwards.”

“Then there is a lake in the center.”

“So I should suppose.”

“It is more than likely that the lake may be an old crater,” said Summerlee.  “The whole formation is, of course, highly volcanic.  But, however that may be, I should expect to find the surface of the plateau slope inwards with a considerable sheet of water in the center, which may drain off, by some subterranean channel, into the marshes of the Jaracaca Swamp.”

“Or evaporation might preserve an equilibrium,” remarked Challenger, and the two learned men wandered off into one of their usual scientific arguments, which were as comprehensible as Chinese to the layman.

On the sixth day we completed our first circuit of the cliffs, and found ourselves back at the first camp, beside the isolated pinnacle of rock.  We were a disconsolate party, for nothing could have been more minute than our investigation, and it was absolutely certain that there was no single point where the most active human being could possibly hope to scale the cliff.  The place which Maple White’s chalk-marks had indicated as his own means of access was now entirely impassable.