Professor Agassiz, in his “General Sketch of the Expedition of the ‘Albatross,’” states that the Galapagos Islands are of volcanic origin, and that their age does not reach beyond the earliest Tertiary period; and his report seems to favor the impression of their having undergone denudation sufficient to slough off large portions of the rims of the older craters, and also the eastern face of Wenman Island. On Hood’s Island, at the time of my visit, its crater had entirely disappeared. The highest portion of the island, which was the probable site of its ancient crater, showed no trace of its former existence; yet at the foot of this low mountain, on its southern side, I saw a large collection of loose bowlders, composed of hard volcanic rock, which were mostly free from soil and other débris, and easily moved from their places, while the spaces afforded by the loose piles of dark basaltic rocks afforded a secure retreat for numerous owls and lizards. Beyond the rocky piles to the southward a horizontal area of land was strewn with bowlders to the sea, which was some two miles distant from the higher land. The bowlders which covered the plain were somewhat smaller than those at the foot of the mountain, as none of the former were more than three or four feet in their longest measurement. They seem to have been formed from thin strata of lava, which were broken in pieces from pressure, such as the action of ice could perform. In fact, the crowded and angular and somewhat worn blocks of lava presented a different appearance from stones thrown from the crater of a volcano, while no such bowlders are found among the recent volcanic eruptions on the islands. The plain so thickly strewn with bowlders, and partly shaded by a tall growth of shrubs, fell off abruptly at the seaside, forming a steep cliff some two hundred feet in height. The rocky floor at the foot of the cliff received such débris as fell from the sea-washed land; yet it contained few bowlders, they having been washed away by the waves soon after falling. At one place a steep, dry ravine penetrated the land from the seashore, which was dangerous to cross on account of the loose stones resting on its sides. Two or three miles further west, on the level land bordering the sea, a large rookery of albatross were brooding their eggs and chicklings. The land on the south side of Albemarle, near the sea, consists of débris from the eroded high lands; and, judging from the crumbling cliffs by the sea, it seems that the land at one time extended further seaward.