For several years I wished to see whether the fumaroles of the lavas had a period of evolution of carbonic acid, as sometimes happens with fumaroles near the craters, but I have always obtained negative results. I often found that the atmosphere on the lavas contained an excess of carbonic acid, but as these lavas had burnt many trees, and it was probable that carbonic acid springs had formed under the lava, I never considered it safe to form any conclusion on the subject. IV. BOMBS, LAPILLI AND ASHES. The bombs ejected from the craters are like those carried down by the lavas, but of smaller size, and they seldomer contain a nucleus similar to those found in the latter. With the bombs properly so called, many pieces of incandescent lava were thrown up, and in their fall went beyond the base of the cone. A quantity of small scoriæ varying in size accompanied these projectiles, and those fragments, which we call _lapilli_, fell at a greater distance. With the lapilli, and sometimes without them, the smoke carried a very minute dust or sand, which is generally called ashes. These ashes, when washed with water, lose soluble constituents which they have collected in the smoke--such as chloride of sodium and other chlorides and often free acids. The insoluble part originates in the detritus of lava, and with the microscope we can detect abundant fragments of those crystals which most frequently occur in the lava of the same eruption. The lavas of 1871, which were eminently leucitic, and almost entirely deprived of pyroxene, resembled the ashes, which appeared to be fragments of crystals of leucite, more or less enveloped in the paste of the lava, so that having triturated the scoriæ of the lava, and looked at the powder through the microscope, it was apparently quite the same as the ashes.