The terrain consisted mostly of thick slime mixed with petrified branches, but it changed little by little near four o'clock in the afternoon; it grew rockier and seemed to be strewn with pudding stones and a basaltic gravel called "tuff," together with bits of lava and sulfurous obsidian. I expected these long plains to change into mountain regions, and in fact, as the Nautilus was executing certain turns, I noticed that the southerly horizon was blocked by a high wall that seemed to close off every exit. Its summit obviously poked above the level of the ocean. It had to be a continent or at least an island, either one of the Canaries or one of the Cape Verde Islands. Our bearings hadn't been marked on the chart-- perhaps deliberately--and I had no idea what our position was. In any case
