Its crater, which is considerable, has given rise to two currents of lava, on one of which the town of Agde is erected, whilst the other, having taken the direction of the sea, has formed a neck of land called Cape Agde, and a little island at a short distance from the shore. M. Marcel de Serres has also described two other rocks to which he assigns the same origin and date; the one that of St. Thibery about four miles north of Agde, the other that of Montferrier near Montpellier. The latter I visited some years ago, and found to consist entirely of compact trap, so that I should be disposed to view it as considerably more ancient. On the Volcanos of Germany. After this general description of the Volcanos of France, I shall proceed to lay before you a short sketch of those which occur distributed over various parts of Germany. Although no active volcanos are found in any part of that extensive country, and the recognition of those which are extinct dates only from the last century, yet those who have visited the spots themselves will feel no more doubt as to their having once existed, than an American who had witnessed the burning mountains of his own hemisphere, but had never heard of those in Europe, would entertain with respect to the real nature of Vesuvius, if landed at its foot when it chanced to be in a tranquil state. This remark applies to no case more completely than to that of the rocks which occur in a district commonly known by the name of the Eyfel, situated between the Rhine and the present frontier of the Netherlands.* *This account of the Rhine volcanos is principally drawn (where the reverse is not stated) from observations made by myself during a tour in that country in the Summer of 1825. This country is bounded on the south-east by the Moselle, on the north-east by the Rhine, on the west by the Ardennes and the other mountains round Spa and Malmedi, and on the south by the level country about Cologne. The fundamental rock which comes to view is clay-slate, associated with greywacké, and with a saccharoid magnesian limestone containing trilobites and other petrifactions, which stamp it as belonging to the transition series. These rocks in a few places support horizontal beds of what appears to be the second or variegated sandstone formation. Scattered however over the greater part of the district alluded to, are a number of little conical eminences, often with craters, the bottoms of which are usually sunk much below the present level, and have thereby in many cases received the drainage of the surrounding country, thus forming a series of lakes, known by the name of "Maars,” which are remarkably distinguished from those elsewhere seen by their circular form, and by the absence of any apparent outlet for their waters. Steininger, a geologist of Treves, who has published the most circumstantial account of this district that has yet appeared, distinguishes these craters into three classes. The first includes those properly speaking known by the name of "Maars,"-volcanos, which have ejected nothing but loose fragments of rock with sand and balls of scoriform lava. In this class are: 1. The Lake of Laach. 3. Three Maars at Daun. 4. Two at Gillenfield. 5. One at Bettenfield. 6. One at Dochweiler. 7. One at Walsdorf. 8. One at Masburck. No. 6 and 7, however, have fallen in. See, for an enumeration of his works, the Appendix. The second class is distinguished from the preceding in consisting of those which have ejected fragments of slag, sometimes loose, and sometimes cemented together into a paste. Of this denomination are: 1. Three Craters at Gillenfield. 2. Two at Bettenfield. 3. One at Gerolstein. 4. One at Steffler. 5. Two at Boos. 6. One at Rolandseck. The third class includes such volcanos as have given out streams of lava as well as ejections of loose substances. Of these latter we may mention : 2. Two at Bertrich (one very small). 3. One at Bettenfield (the Mosenburg). 5. One at Gerolstein. 6. One at Ettringen. Thus the whole number of craters in the Eyfel district, including those of the same date that are scattered along and near the left bank of the Rhine within the limits marked out, appears to be not less than thirty. The sides of these craters, wherever their structure was discernable, appeared to me to be made up of alternating strata of volcanic sand and fragments of scoriform lava, dipping in all directions away from the centre at a considerable angle, and the same kind of material has in many instances so accumulated round the cones, as to obliterate in great measure the hollow between them, and to raise the level of the country nearly up to the brim of the craters. The formation of these cones seems likewise to have been in some instances followed by an ejection of substances of a pumiceous character, and the same kind of material (whether derived from these or from some antecedent eruptions, will be afterwards considered), is spread widely over the country bordering on the Rhine, either in loose strata alternating with beds of a loamy earth, derived probably from substances in a minute state of division thrown out by the same volcano, and mixed up into a paste with water; or else forming masses of considerable thickness, in which the fragments of pumice are intermixed with the latter substance, and constitute together with it a coherent mass known by the name of Trass. The volcanos of the Eyfel are also, as above noticed, accompanied by streams of lava, but these have not, in my opinion, like the generality of those seen elsewhere, been satisfactorily traced to the craters, but seem rather to have flowed from the sides or base of the mountains with which they are respectively connected. These Coulées, like the volcanic cones themselves, are sometimes almost buried under heaps of matter subsequently ejected, so that in the lava of Niedermennig, the quarry, from whence the millstones are obtained, is worked at a depth of eighty feet from the present surface. They are in some cases analogous to the ejections of existing volcanos, but at others they possess more of a basaltic character, being freer from cells than true lavas generally are, although it can be demonstrated that they too are (geologically speaking) of modern formation, inasmuch as they follow the inclination of the vallies, and must therefore have flowed since the latter were excavated. The above remarks may suffice for a general description of the Eyfel volcanos. I shall now therefore proceed to particularise two or three of the more important. Beginning with the country nearest the Rhine, which is known by the name of the Maifeld, let us first consider the remarkable crater called the Lake of Laach, which occurs near Andernach, a few miles west of the Rhine. The lake of Laach is perfectly round, and embraces a circumference of two miles. Its sides are overgrown with wood from the level of the water up to the brim of the LAKE OF LAACH. crater, which is reached externally by a gentle ascent not at all in proportion to the depth of the internal cavity. The thickness of the vegetation renders it difficult to discover the nature of the subjacent rock, but it appears to consist of a black cellular lava full of augite. Besides this however, the sides of the crater present numerous loose masses, which appear to have been ejected, and consist of glassy felspar, ice-spar, sodalite, hauyne, spinellane, and leucite. It will be seen, when I come to speak of the neighbourhood of Naples, how remarkable is the resemblance between these products and the ejected masses found on the slope of Vesuvius." Not much above a mile from this spot is the rock of Niedermennig, so extensively quarried for millstones; but though this has all the appearance of a stream of lava, no one has as yet succeeded in tracing it either to Laach or to any other neighbouring volcano. The lava is divided by vertical fissures into irregular columnar masses, some twenty feet in height, and these columns cut horizontally, and having their angles rounded off, are fashioned into millstones,* for which they are well adapted from the unevenness of their fracture, derived from the infinite number of minute cells distributed through the substance of the rock. It is only the middle portion however of this bed which can be so employed, for in the upper not only are the pores too considerable, but the concretions, being smaller than they are below, scarcely afford masses of sufficient magnitude for the purpose intended. This difference arises from the greater size of the fissures The same use appears to have been made of the Lavas of Etna by the ancients. See Corn. Sev. Etna. Quin etiam vario quædam sub nomine saxa Toto monte liquant; illis custodia flammæ D |