The island contains active volcanoes, as I am informed, and in the immediate vicinity of the cave are solfataras, from which steam constantly arises, and the soil is said to be warm to the touch. The rock is of a whitish and ferruginous color and sharp grain. Specimens examined by Dr. Endlich, of the Smithsonian Institution, prove to be a siliceous sinter, containing a little alumina and soda, and some hydrous sesquioxide of iron. In the spectroscope traces of lithium and potassium and, possibly, a trace of lime were seen. From this, and from the fact that the atmosphere of the cave is said to have been quite hot, rendering it uncomfortable to remain in, it is possible that the cave itself may be the crater of a small extinct solfatara.