exit of the
canal, and if may become necessary to distribute the power of these wheels
along the works. In these regions of difficult access and few resources it
is necessary to dispense with complicated apparatus, and one might in such
a case, it would seem, try electric motors, whose installation would be
easy. An exploitation in accordance with these ideas was begun for the
first time in 1883 upon the Ribeirao de Inferno at Portao de Ferro. We
shall describe it.

Once established in the country, the first thing to do is to form roads so
as to secure communications with the neighboring villages and forests, and
afterward to cut down trees for building houses. These latter are usually
constructed, for these works, of untrimmed wood and mud, with thatched
roof. There were thus constructed at Portao de Ferro a few kilometers of
roads, then some houses for the engineers and special workmen, barracks
for 200 laborers, stores, kitchens, etc., a forge, and a shop with a lathe
and a saw run by a wheel at the side. It was afterward necessary to repair
the old lateral canal which had been dug out of the rock in the times of
the Royal Extraction, but which had been torn open for a considerable
length. This necessitated the erection of tight walls of dry stone, grass,
and mud, for a length of 200 meters, and with thicknesses of from 6 to 10
meters.

In order to divert the water into this canal, it was necessary to raise
its level 5 meters. The dam, then, had to support a strong pressure, and
it could not be built upon sand. It therefore became necessary to build a
temporary dam and to turn the river into a plank flume, so as to make it
possible to dig at the location of the permanent dam in order to reach a
solid bottom at a depth of nearly 4 meters. The permanent dam thus had a
total height of 10 meters, with a thickness of 15 at the base and 7 at the
top. It was constructed of dry stone, grass, and earth, with the addition
of strong wood-work. The rocks upon which it had to be built were full of
fissures, and when it was desired to close it great leakages of water
occurred, which came near ruining it and necessitated the construction of
a second wall behind it and a talus of earth in front. The dam as shown in
Fig. 1, when finished, had a thickness of 25 meters at the base. It was
closed on the second of July, and had a storage capacity of 55,000 cubic
meters.

The principal excavation was begun at the point where the bed wa