volcanoes) of Agrigentum, which, as I have already mentioned, eject argillaceous mud with a loud noise. It is much to be regretted, in reference to this subject, that the work of Theophrastus [Greek words] 'On the Volcanic Stream in Sicily', to which Diog. Laert., v., 49, refers, has not come down to us. p 238 The different volcanoes over the earth's surface, when they are considered independently of all climatic differences, are acutely and characteristically classified as central and linear volcanoes. Under the first name are comprised those which constitute the central point of many active mouths of eruption, distributed almost regularly in all directions; under the second, those lying at some little distance from one another, forming, as it were, chimneys or vents along an extended fissure. Linear volcanoes again admit of further subdivision, namely, those which rise like separate conical islands from the bottom of the sea, being generally parallel with a chain of primitive mountains, whose foot they appear to indicate, and those volcanic chains which are elevated on the highest ridges of these mountain chains, of which they form the summits.* [footnote] *Leopold von Buch, 'Physikal. Beschreib. der Canarischen Inseln', s. 326-407. I doubt if we can agree with the ingenious Charles Darwin ('Geological Observations on Volcanic Islands', 1844, p. 127) in regarding central volcanoes in general as volcanic chains of small extent on parallel fissures. Friedrich Hoffman believes that in the group of the Lipari Islands, which he has so admirably described, and in which two eruption fissures intersect near Panaria, he has found an intermediate link between the two principal modes in which volcanoes appear, namely, the central volcanoes and volcanic chains of Von Buch (Poggendorf, 'Annalen der Physik', bd. xxvi., s. 81-88). The Peak of Teneriffe, for instance, is a central volcano, being the central point of the volcanic group to which the eruption of Palma and Landerote may be referred. The long, rampart-like chain of the Andes, which is sometimes single, and sometimes divided into two or three parallel branches, connected by various transverse ridges, presents, from the south of Chili to the northwest coast of America, one of the grandest instances of a continental volcanic chain. The proxiimity of p 239 active volcanoes is always manifested in the chain of the Andes by the appearance of certain rocks (as dolerite, melaphyre, trachyte, andesite, and dioritic porphyry), which divide the so-called primitive rocks, the transition slates and sandstones, and the stratified formations. the constant recurrence of this phenomenon convinced me long since that these sporadic rocks were the seat of volcanic phenomena, and were connected with volcanic eruptions. At the foot of the grand Tunguragua, near Penipe, on the banks of the Rio Puela, I first distinctly observed mica slate resting on granite, broken through by a volcanic rock.