immediately from granite mountains is in Europe, as well as in the New
Continent, a most curious phenomenon.* (* Warm springs equally pure
are found issuing from the granites of Portugal, and those of Cantal.
In Italy, the Pisciarelli of the lake Agnano have a temperature equal
to 93 degrees. Are these pure waters produced by condensed vapours?)
How can we explain the origin of the sulphuretted hydrogen? It cannot
proceed from the decomposition of sulphurets of iron, or pyritic
strata. Is it owing to sulphurets of calcium, of magnesium, or other
earthy metalloids, contained in the interior of our planet, under its
rocky and oxidated crust?

In the ravine of the hot waters of Mariara, amidst little funnels, the
temperature of which rises from 56 to 59 degrees, two species of
aquatic plants vegetate; the one is membranaceous, and contains
bubbles of air; the other has parallel fibres. The first much
resembles the Ulva labyrinthiformis of Vandelli, which the thermal
waters of Europe furnish. At the island of Amsterdam, tufts of
lycopodium and marchantia have been seen in places where the heat of
the soil was far greater: such is the effect of an habitual stimulus
on the organs of plants. The waters of Mariara contain no aquatic
insects. Frogs are found in them, which, being probably chased by
serpents, have leaped into the funnels, and there perished.

South of the ravine, in the plain extending towards the shore of the
lake, another sulphureous spring gushes out, less hot and less
impregnated with gas. The crevice whence this water issues is six
toises higher than the funnel just described. The thermometer did not
rise in the crevice above 42 degrees. The water is collected in a
basin surrounded by large trees; it is nearly circular, from fifteen
to eighteen feet diameter, and three feet deep. The slaves throw