he Peruvian guano a more arid
manure than the African, as fewer of the saline particles of the former
being in solution, they are consequently less subject to evaporation.

From 3 deg. 35' to 21 deg. 48' south latitude, a plain of sand, 540 leagues
long, and varying from 3 to 20 leagues in breadth, stretches along the
coast of the Pacific Ocean. It is intersected by chains of small
hillocks, which, extending westward from the Cordilleras, gradually
diminish in height, and either become blended with the plain, or form
abrupt promontories, which project into the sea. Between the river Loa,
which marks the southern frontier of the Peruvian coast, and the Tumbez,
on the northern boundary, fifty-nine rivers, great and small, pass
through the line of coast. Proceeding from the avalanches of the Andes
or the small alpine lakes, they force their way through narrow
mountain-valleys, irrigate the waste grounds, and then, after brief
courses, flow into the great ocean.

A fine light yellow drift sand covers hill and dale. It is only where
rivers intersect the plain that oases of luxuriant vegetation are
formed. The peril of traversing these plains is greatly increased by
the movability of the sand and the _Medanos_. The strong winds raise
immense clouds of dust and sand. The sand rises in columns of from
eighty to a hundred feet high, which whirl about in all directions, as
if moved by magic. Sometimes they suddenly overshadow the traveller, who
only escapes from them by rapid riding.

The medanos are hillock-like elevations of sand, some having a firm,
others a loose base. The former, which are always crescent-shaped, are
from ten to twenty feet high, and have an acute crest. The inner side is
perpendicular, and the outer or bow side forms an angle with a steep
inclination downward. When driven by violent winds, the medanos pass
rapidly over the plains. The smaller and lighter ones move quickly
forwards before the larger ones; but the latter soon overtake and crush
them, whilst they are themselves shivered by the collision. These
medanos assume all sorts of extraordinary figures, and sometimes move
along the plain in rows forming most intricate labyrinths, whereby what
might otherwise be visible in the distance is withdrawn from the view of
the traveller. A plain often appears to be covered with a row of
medanos, and some days afterwards it is again restored to its level and
uniform aspect. Persons who have the greatest experie