Page:Africa by Élisée Reclus, Volume 3.djvu/52

 needle, and take the name of olhos, or "eyes;" but the most copious spring is the caldeira, or "cauldron," which ejects with a rumbling noise a liquid stream to a height of over three feet above the level of the basin. From the encircling rocks, worn and bleached by the acids, there escape some boiling rivulets, and even in the bed of the main stream hot springs are revealed by the bubbles and vapours

rising above the surface. The temperature of the waters, some of which are utilised for hot baths, varies considerably, ranging from 70° F. to 208° F., which is neatly that of boiling water. The "furnaces," which differ also if their mineral properties, have undergone no change for the last three hundred years beyond the gradual deposit of thick silicious layers in which plants are petrified. Large trees have thus become rapidly fossilised.