de to England. It was not, however,
till some ten or twelve years later that the Peruvian Government, to
whom they then belonged,[204] seems to have recognised their value. The
most important deposits are found in the vicinity of the town of
Iquique, which is the chief nitrate port of South America. It is a
somewhat striking fact that this substance, which has conclusively
proved itself to be the most potent of all known artificial agents in
the promotion of vegetable growth, should be found in a district utterly
lacking the slightest traces of vegetation of any kind. Lest such a
statement should seem to savour of irony, we hasten to explain that the
singular barrenness of this part of the country is largely due to the
character of its climate, the deposits occurring in the midst of sandy
deserts,[205] on which rain never falls.

_Their Origin._

The origin of these nitrate-fields is a geological problem of very
considerable interest, the difficulty of which is greatly enhanced by
their altitude--3000 to 4000 feet above the sea-level--and their
distance inland, which amounts in some cases to eighty or ninety miles
from the sea-coast. The nitrate deposits are not the only saline
deposits found in Chili. According to the late David Forbes,[206] they
are not to be confused with other saline formations, which appear at
intervals scattered over the whole of that portion of the western coast,
on which no rain falls. The latter stretch from north to south for a
distance of more than 550 miles--their greatest development being
between latitudes 19 deg. and 25 deg. south. The depth to which they extend
downwards varies considerably. Most of them, however, are of a very
superficial character, and "they always show signs of their existence by
the saline efflorescence seen on the surface of the ground, which often
covers vast plains as a white crystalline incrustation, the dust from
which, entering the nostrils and mouth of the traveller, causes much
annoyance, whilst at the same time the eyes are equally suffering from
the intensely brilliant reflection of the rays of a tropical sun." These
saline incrustations, or _salinas_, as they are generally called, are
chiefly composed of salts of lime, soda, magnesia, alumina, and of
boracic acid. Their composition would lead one to attribute their origin
to the evaporation of salt water; for, with the single exception of
boracic acid,[207] all the mineral substances are such as would b