270 REPORT ON THE DENEHOLE EXPLORATION
most ancient and wide-spread, in an admirable historical introduction
to his proposal.
M. L. Doyere, following these able writers after a long period,
published in 1862 an account of a regular investigation he had just
concluded into the silos of certain parts of Spain. He also advocated
an improvement of his own in his brochure, "Ensilage des Grains."
The latest improvement was that suggested by M. Louvel in 1867,
who proposed to place the corn in iron receivers, and exhaust the air.
In Spain, then, the silo is common. It is there an excavation
which generally has the form of an egg or carafe, i.e., a water jug.
The orifice is circular, and of the size which just admits a man. The
silo enlarges downwards from the surface, sometimes with a few feet
of shaft, to about three quarters of the total depth, which is the widest
part, while others widen into vaults. Sometimes a circle of brick
(occasionally there is more masonry) is put round the mouth, which
is closed with a flat stone or piece of wood, and a little heap of soil
is raised over all to throw off the rain. Occasionally sheds are
erected over the pits. Silos are usually placed on elevated ground.
The soil selected is generally in compact clay or hardened sand.
M. Jourdain recommends pits in "earth" (terre) as preferable
from its purifying or disinfecting properties.
While single silos are common, it is the custom to accumulate
them in hundreds, and even thousands, in or about cities, when
a suitable bed has been found to dig them in. In some places
these collections are grouped into definite areas called Sileras, which
are occasionally surrounded with a wall, and even have a watch tower.
In one place, Boursasot, the whole surface of the enclosure is paved
with flagstones. The dimensions vary from six or eight to between
thirty and forty or more feet deep, and while some are so narrow as
scarcely to amount to more than wells, others widen out to fifteen
feet or more. The depth is a matter of indifference if water does
not stand within four or five feet from the bottom. The majority of
silos contain under 100 fanegas—one fanega equals 1.55 bushels.
From this the size runs up to 8,000 hectolitres, or about 27,000 cubic
feet.
The floor of the silo is prepared by spreading it with bavins and
matting, while the sides are covered with long straw, fern, or mats.
Where the soil is unsuitable, the silos are built in masonry under the
soil, this is also a common custom where a regular trade in corn
requires permanency in matters connected with the business. Spain