before they become available for
the plant's uses.

4. That, at present market prices, nitrate of soda may be safely
affirmed to be the cheapest form of nitrogenous manure.

5. That nitrate of soda, in addition to its direct value as a manure,
probably exercises a slight influence on the mechanical properties of
the soil, by increasing its compactness and water-absorbing capacities;
that it further tends to promote deep roots, and thus to increase the
soil area whence the plant may derive its nourishment, at the same time
rendering the plant more able to withstand the injurious influence of
drought.

6. That a plentiful supply of the other manurial constituents should be
present in the soil, if nitrate of soda is to exercise its full value.

7. That it may be profitably applied in the case of nearly all kinds of
crops, but that great care should be taken as to the mode of its
application. That this should be almost invariably as a top-dressing,
and that it should be applied in several doses if possible.

8. That its effects can be regarded as lasting only during the first
year after application.

FOOTNOTES:

[202] This substance is also largely known under the name Chili
saltpetre, to distinguish it from potassium nitrate or common saltpetre.

[203] See Appendix, p. 351.

[204] We may remind our readers that these nitrate deposits were largely
the cause of the late war between Chili and Peru, which resulted in the
cession to Chili by Peru of the province of Tarapaca, where the most
important deposits are situated.

[205] The other nitrate deposits are found in the provinces of
Antofagasta and Atacama, and a certain amount of the refined article is
exported from these places. The amount, however, is inconsiderable as
compared with that which comes from the province of Tarapaca.

[206] See his elaborate article on the Geology of Bolivia and Peru,
published in the 'Quarterly Journal of the Geological Society' for
November 1860.

[207] The source of the boracic acid is probably volcanic.

[208] A friend of the present writer, who has visited this part of the
west coast of South America, informs him that at one point of the coast
at Mejillones (in Bolivia) he could trace the remains of no fewer than
twelve distinct sea-beaches, situated at different distances from the
sea, and rising to an altitude of 2500 feet.

[209] In this change, lime derived from the sea-shells would play an
important part. Modern r