Balloons, however, render access possible,
both to its summit and to its cave-pierced sides. It is the home of
enormous flocks of white birds, which resemble in form the heron
rather than the eider duck, but which, like the latter, line with down
drawn from their own breasts the nests which, counted by millions,
occupy every nook and cranny of the crystalline walls, about ten miles
in circumference. Each of the nests is nearly as large as that of the
stork. They are made of a jelly digested from the bones of the fish
upon which the birds prey, and are almost as white in colour as the
birds themselves. Freshly formed nest dissolved in hot water makes
dishes as much to the taste of Martialists as the famous bird-nest
soup to that of the Chinese. Both down and nests, therefore, are
largely plundered; but the birds are never injured, and care is taken
in robbing them to leave enough of the outer portion of the nest to
constitute a bed for the eggs, and encourage the creatures to rebuild
and reline it.

One harvest only is permitted, the second stripping of feathers and
the rebuilt nest being left undisturbed. The caverns are lined with a
white guano, now some feet thick, since it has ceased to be sought for
manure; the Martialists having discovered means of saturating the soil
with ammonia procured from the nitrogen of the atmosphere, which with
the sewage and other similar materials enables them to dispense with
this valuable bird manure. Whether the white colour of the island,
perceptible even in a large Terrestrial telescope, is in any degree
due to the whiteness of the birds, their nests, and leavings, or
wholly to reflection from the bright spar-like surface of the rock
itself, and especially of the flat table-like summit, I will not
pretend to say.

From this point we held our course south-westward, and entered the
northernmost of two extraordinary gulfs of exactly similar shape,
separated by an isthmus and peninsula which assume on a map the form
of a gigantic hammer. The strait by which each gulf is entered is
about a hundred miles in length and ten in breadth. The gulf itself,
if it should not rather be called an inland sea, occupies a total area
of about 100,000 square miles. The isthmus, 500 miles in length by 50
in breadth, ends in a roughly square peninsula of about 10,000 square
miles in extent, nearly the whole of which is a plateau 2000 feet
above the sea-level. On the narrowest point of the isthmus, just