The terrace closest to the land, known as the continental shelf, has an average depth of 600 ft., and connects Australia, New Guinea, and Tasmania in one unbroken sweep. Compared with other continents, the Australian continental shelf is extremely narrow, and there are points on the eastern coast where the land plunges down to oceanic depths with an abruptness rarely paralleled.
The other three sides are formed by a retaining wall, varying in height with the slope of the ground from 14 to 41 ft.; on the west side a magnificent double stair, of very easy steps, leads to the top. On this terrace are the ruins of a number of colossal buildings, all constructed of dark-grey marble from the adjacent mountain.
Two miles north-east is the famous Silla de Caracas, whose twin summits, like a gigantic old-fashioned saddle (silla), rise to an elevation of 8622 ft.; and the Naiguete, still farther eastward, overlooks the valley from a height of 9186 ft.
The larger members of the group, several of which attain an elevation of 2000 to 2500 ft., are Albemarle or Isabela (ioo m.
The contrast between this low zone and the upper zone of rich vegetation (above about Boo ft.) is curiously marked.