The high hills flanking the desert near
Arequipa are too steep to allow the
dunes to proceed farther. They there
fore pile up in a sort of a sandy cem
etery at the eastern edge of the Pam
pa. Before they reach the end, how
ever, and as the hills deflect the air
in different directions, dunes occasion
ally advance over or threaten the rail
way line. The method of avoiding the
threatened obstruction is simple but
effective. A couple of men go out with
long-handled spades and a wheelbar
row and collect loose pebbles and grit
from the surface of the Pampa. This
they proceed to scatter in a thin layer
over the back of the unfortunate dune.
The pebbles arrest the action of the
ripples and so Interfere with the even
circulation of the sand particles, which
is apparently as essential to the prog
ress of the dune as the circulation of
blood to a human being. Very short
ly the dune assumes a lopsided shape,
sagging where the debris has been cast
upon it, and offering, instead of a well
rounded back, a breach to the-action
of the wind. The progress of disinte
gration is fairly rapid, and at the
end nothing Is left on the Pampa ex
cept the original wheelbarrow loads of
grit and pcbblc3 which suffice to ex*
ercise the monster
The dunes advance over pebbles and
stones without disturbing their posi
tion. I noticed immediately behind
large dunes scattered stones
that obviously had not shifted from
their bed, just as pebbles may lie se
cure on the seashore In the swell of
the breakers. Generally speaking, the
smoother the surface of the Pampa
and the higher the wind, the larger
and more perfect becomes the dune.
Did His Share.
