the color is a rusty red, as if tinged by
oxide of iron. The Guano becomes progressively more and more solid from
the surface downward, a circumstance naturally accounted for by the
gradual deposite of the strata, and the evaporation of the fluid
particles. Guano is found on all the islands, and on most of the
uninhabited promontories of the west coast of South America, especially
in those parts within the tropics. I have often been assured that beds
of Guano several feet high, covered with earth, are found inland at some
distance from the sea; but I never met with any, and I have some doubt
of the correctness of the statement. If, however, these inland strata
really exist, I am inclined to believe that they can only be found on
hilly ground; and in that case they afford strong evidence of a
considerable elevation of the coast.

Guano is formed of the excrements of different kinds of marine birds,
as mews, divers, sheerbeaks, &c.; but the species which I can name
with more precision are the following:--_Larus modestus_, Tsch.;
_Rhinchops nigra_, Lin.; _Plotus Anhinga_, Lin.; _Pelecanus thayus_,
Mol.; _Phalacrocorax Gaimardii_, and _albigula_, Tsch. (_Pelecanus
Gaimardii_, Less., _Carbo albigula_, Brandt), and chiefly the _Sula
variegata_, Tsch.

The immense flocks of these birds as they fly along the coast appear
like clouds. When their vast numbers, their extraordinary voracity, and
the facility with which they procure their food, are considered, one
cannot be surprised at the magnitude of the beds of Guano, which have
resulted from uninterrupted accumulations during many thousands of
years. I kept for some days a living _Sula variegata_, which I fed
abundantly with fish. The average weight of the excrement daily was
from 3-1/2 to five ounces. I have no doubt that when the bird is in a
state of freedom the weight must be much greater, for these birds are
constantly plunging into the sea, in order to devour the fishes which
they find in extraordinary masses around all the islands. When an
island is inhabited by millions of sea-birds, though two-thirds of
the guano should be lost while flying, still a very considerable
stratum would be accumulated in the course of a year.

The marine birds nestle on the uninhabited islands, or on rocks near the
shore; but they never settle on the flat beach, or any place distant
from it inland. On this fact, I ground my conjecture that those beds of
guano in the interior, which may ha