four o’clock in the
afternoon
Sometimes an unpredictable irregularity in the seafloor would force the Nautilus to slow down , and then it would glide into the narrow channels between the hills with a cetacean 's dexterity . If the labyrinth became hopelessly tangled , the submersible would rise above it like an airship , and after clearing the obstacle , it would resume its speedy course just a few meters above the ocean floor . It was an enjoyable and impressive way of navigating that did indeed recall the maneuvers of an airship ride , with the major difference that the Nautilus faithfully obeyed the hands of its helmsman . 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 .