ed pebbles, mixed with sand.
This gravel, which is characterized in the first place by the fact that
all its elements are rounded, and next by the presence of a large number
of minerals (among which the most important are all the oxides of
titanium, different oxides of iron, tourmaline, and a whole series of
hydrated phosphates of complex composition), is called in the language of
the country _cascalho_. It is the matrix of the diamond, and the latter is
extracted from it by washing. It is arranged in roundish masses upon the
beds of the rivers, and is met with at depths ranging from a few
decimeters up to 25 and 30 meters.

The same material, with the same name, is also found deposited at all
heights upon small terraces at the sides of the valleys through which the
rivers flow. It is coarser and less rolled, and has very likely been
deposited by risings of the rivers during the period when the valleys were
being formed. These deposits bear the name of _gupiarras_. Finally, it is
found in a still coarser state, mixed with red earth and deposited in
horizontal strata upon the upper plateau. It is then called _gorgulho_.

Of these different deposits, the most important are those of the river
beds, the material here having undergone a true mechanical preparation and
being richer. These are the deposits that have been the object of the most
important exploitations.

The year is divided into two distinct seasons--the dry, from May to
September, during which rain is exceptional, and the rainy, from October
to April. As water is necessary for all the operations, no work can be
done upon the high plateaux except through rain water stored up in large
reservoirs. These beds form what are called the "rainy season washings."
In the rivers the working of the beds requires a preliminary drying, which
is effected by diverting the river's course. Now in all this rocky and
denuded region the water that falls runs immediately to the river, and
causes terrible freshets therein; so operations capable of keeping the bed
dry would be out of proportion to the probable results of the
exploitation, whence it follows that the latter is only possible in dry
weather, and these deposits are therefore called "dry season washings."

These deposits are still worked in our day as they were in the time of the
Portuguese. In order to dry the bed a dam is constructed, and the river is
either diverted into a plank flume supported by piles, or into a cana