About four o'clock
The species of fishes here did not differ much from those already noticed . There were rays of giant size , five yards long , and endowed with great muscular strength , which enabled them to shoot above the waves ; sharks of many kinds ; amongst others , one fifteen feet long , with triangular sharp teeth , and whose transparency rendered it almost invisible in the water . Amongst bony fish Conseil noticed some about three yards long , armed at the upper jaw with a piercing sword ; other bright-coloured creatures , known in the time of Aristotle by the name of the sea-dragon , which are dangerous to capture on account of the spikes on their back . About four o'clock , the soil , generally composed of a thick mud mixed with petrified wood , changed by degrees , and it became more stony , and seemed strewn with conglomerate and pieces of basalt , with a sprinkling of lava . I thought that a mountainous region was succeeding the long plains ; and accordingly , after a few evolutions of the Nautilus , I saw the southerly horizon blocked by a high wall which seemed to close all exit . Its summit evidently passed the level of the ocean . It must be a continent , or at least an island -- one of the Canaries , or of the Cape Verde Islands .