Central Africa. From these cones escaped gaseous and bituminous springs, which are called mud volcanoes, though volcanic action has nothing to do with their production. The eruption is simply a mixture of mud, gypsum, chalk, pyrites, with petroleum even, which, under the pressure of carbonetted, or sometimes phosphoretted, hydrogen gas, escapes with considerable violence. These little heaps, which are raised by degrees, give way to permit the eruptive matter to escape, and afterwards fall in, when the tertiary formations are exhausted, in a space of time of greater or less duration.
The hydrogen gas produced under these conditions is due to the slow, but continuous decomposition of petroleum mixed with various other substances. The rocky region in which it is enclosed is finally broken up under the action of water (rain or springs), the filtration of which is continuous. Then the effusion ceases, just as the effervescence of champagne will cease as the elasticity of the gas is exhausted. These cones of ejected matter open in great numbers in the peninsula of Taman. There are other localities in the peninsula of Kertsch, for instance, where they may be observed; but our travellers did not see them, for they do not exist near the high road.
However, the travellers passed here between the great mounds surrounded with fumes, in the midst of the outpourings of liquid mud. Sometimes the pedestrians were obliged to approach so close to them that they received puffs of the gas right in their faces, which gave them a most disagreeable sensation, and was of a most unpleasant odour.
"Eh," said Van Mitten, who recognized the presence of gas, "we are in danger here. I trust there will be no explosion."
"You are right," replied Ahmet. "We must be cautious, and ought to extinguish the lamps."
The postillion, who was doubtless conversant with the route, was evidently of the same opinion, for the lamps were suddenly extinguished.
"Mind you do not smoke, you fellows," cried Ahmet to the servants.
