Diablo, are much less lofty, and contain, like the promontory of La
Cabrera, and the little detached hills in the plain, gneiss and
mica-slate, including garnets.

In these lower mountains, two or three miles north-east of Mariara, we
find the ravine of hot waters called Quebrada de Aguas Calientes. This
ravine, running north-west 75 degrees, contains several small basins.
Of these the two uppermost, which have no communication with each
other, are only eight inches in diameter; the three lower, from two to
three feet. Their depth varies from three to fifteen inches. The
temperature of these different funnels (pozos) is from 56 to 59
degrees; and what is remarkable, the lower funnels are hotter than the
upper, though the difference of the level is only seven or eight
inches. The hot waters, collected together, form a little rivulet,
called the Rio de Aguas Calientes, which, thirty feet lower, has a
temperature of only 48 degrees. In seasons of great drought, the time
at which we visited the ravine, the whole body of the thermal waters
forms a section of only twenty-six square inches. This is considerably
augmented in the rainy season; the rivulet is then transformed into a
torrent, and its heat diminishes for it appears that the hot springs
themselves are subject only to imperceptible variations. All these
springs are slightly impregnated with sulphuretted hydrogen gas. The
fetid smell, peculiar to this gas, can be perceived only by
approaching very near the springs. In one of these wells only, the
temperature of which is 56.2 degrees, bubbles of air are evolved at
nearly regular intervals of two or three minutes. I observed that
these bubbles constantly rose from the same points, which are four in
number; and that it was not possible to change the places from which
the gas is emitted, by stirring the bottom of the basin with a stick.
These places correspond no doubt to holes or fissures on the gneiss;