Besides the above named geyser regions there is another region on the shores of Celebes, and a small region on San Miguel, in the Azores Islands, in the Atlantic Ocean. Besides hot springs and mud volcanoes there are two other phenomena connected with volcanic action that we will now briefly describe. When eruptions take place and the lava begins to flow down the side of a mountain, the different vapors and gases with which the lava is charged begin to escape or pass out from the boiling or fused mass. When these substances are of such a character that they produce fumes, or the vapors of various chemical substances, that become solid on cooling, they form what are called _fumaroles_, a word derived from a Latin word meaning "to smoke." For the greater part, fumaroles are found on the edge of craters, but sometimes are found in cavernous places either in the crater or in the lava streams. There is, still, another class of openings through which only sulphurous vapors escape. These are called _solfataras_, a word derived from the Italian word _solfo_, or sulphur. Solfataras are generally found in regions distant from volcanic action. In the materials that escape from recently ejected lava, or molten lava, the temperature is high enough to volatilize many of the solid ingredients. But where the temperature is low, only sulphur vapors are driven off. It is for this reason that fumaroles are only found around the craters of active volcanoes, or on the lines of cracks or crevices of the lava stream where the temperature is very high. [Illustration: FIG. 38. BEE HIVE GEYSER OF ICELAND _From Dana's Manual of Geology_] Besides water vapor and sulphurous vapors there are other substances that escape from the earth in volcanic districts. Sulphurous acid, together with hydrogen and nitrogen escape from nearly all lava. At Vesuvius chlorine gas is given off. This, however, as soon as it passes into the atmosphere becomes changed into hydrochloric acid. Sulphurous acid is frequently changed into sulphuric acid, which, combining with various substances, forms such materials as _gypsum_, or sulphate of lime, the chemical name for plaster of Paris; sulphate of soda or _Glauber's salt_; sodium chloride or _common table salt_; and _sal ammoniac_. You will remember in reading the description of Vulcano, in the Grecian Archipelago, that some of these products were collected at the chemical works that had been established on the volcano. When a volcanic mountain is for the time being passing from an active to an extinct condition, it is sometimes said to be in the _fumarole stage_, since the presence of the fumaroles are the only indication of its activity. The volcanic heat is still great. When it reaches a still greater decline, the fumaroles disappear, and only solfataras are left. The amount of heat is now only sufficient to produce sulphur vapors and the vapor of water. This is called the _solfatara stage_.