NEAR HEIDelburg. nerally most compact, were first thrown up by the agency of a volcano, and that the cellular matters being subsequently ejected, arranged themselves around them in successive strata. The volcanic operations, taking place with the greatest intensity round the area now occupied by the Vogelsgebirge and the other basaltic groupes, would cover completely with their products the surface of the subjacent rock; whilst at a greater distance from the sphere of their activity, isolated cones of basaltic matter would be occasionally thrown up, as at Eisenach, at Cassel, in the neighbourhood of Frankfort, and on the west bank of the Rhine. Besides the volcanos above enumerated, there occur near the borders of the Rhine, but higher up the stream, other rocks which are said to have a similar origin. In the Odenwald, a group of hills in the neighbourhood of Heidelburg, from the midst of the new red sandstone, rise some eminences in which basalt is associated with augite rock (dolerite of Brongniart), and contains nepheline (Katzenbuckel), mica, mesotype, olivine, and titaniferous iron ore. It is probably analogous to the Hessian basalts. The augite rock is seen in situ at Gaffstein, the basalt containing olivine at Pechsteinkopf and Durkheim.* Near Freyburg in the Brisgaw is the group of the Kaiserstuhl, of which Dr. Boué has given an account in his memoir on the South-west of France. It appears from his report to be a mass of augite rock with excess of felspar (dolerite felspathique) thrown up from the midst of the plastic clay. The highest mountain in the groupe is the Kaiserstuhl, which rises to the height of about 1120 feet above the river, and this with the other eminences composed of the same materials are ranged in an elliptical form round a valley. These rocks offer no trace of craters or streams of lava, *See Leonhard Taschenbuch for 1822. + Annales des Sciences Naturelles, August, 1824. BRISGAW. but are associated, especially near the surface, with cellular lava, containing calcareous spar and mesotype. Hyalite occurs in the cavities, and incrusting the surfaces of the rock. Tufaceous matters are not common, but occur along the Rhine at Breisach, where they seem, like those near Eisenach, to be contemporaneous with the augite rock. I am also assured that the rock of Kaiserstuhl is partially covered with a calcareous deposit, the only instance I believe among the Rhine volcanos in which this occurs. Saussure,+ who visited this groupe in 1794, and appears to have been somewhat swayed by the authority of Werner, is nevertheless compelled to acknowledge the volcanic origin of the rocks about Limburg, which are in part penetrated with oval cells, in great measure void, and of the tuff about Echardberg, which contain fragments of scoriform lava. The origin of the basalt itself he considers doubtful, but there are few at the present day who will concur with him in that opinion, considering how intimate appears to be the connection between the porous and compact rocks in this locality. Upon the whole the groupe of the Kaiserstuhl may be set down as belonging to the same æra as the basalt of the Westerwald, and the trachyte of the Seven Mountains. A few miles to the north of the Lake of Constance is the commencement of another series of basaltic and porphyritic cones, first seen at Hohentwiel and in several detached hills contiguous, which rise from the midst of the (Jura?) limestone formation. They consist in part of clinkstone, and in part of basalt, accompanied with tuff containing fragments of trap rock (always compact) as well as of gneiss, limestone, quartz, &c. all cemented by a wacke-like paste of a ochrey colour. In the hill of Magdeburg, a passage is said to exist be + Journal de Physique, vol. 44. F * tween the clinkstone and the basalt; at Hohentwiel, the former contains veins and nodules of natrolite, together with opal, pitchstone and hyalite. In Wirtemburg basalt occurs both in overlying masses, and dykes, in various places along the chain of the Rauhe Alp south of Tubingen, and is perhaps connected with the rocks of Swabia above described. Professor Scubler + remarks, that the horizontal stratification of the limestone composing that country is destroyed, wherever the basalt approaches it. The chief localities are Linsenhofen, Faisel, Dettingen, Jusiberg near Urach, Grabenstetten, Donstetten, the valley of Guttenburg, Rauberstege near Brachen, near Dottingen, Offenhausen, Ehningen, and Donaueschingen. Basaltic rocks, many of which are probably referable to the same class as those already noticed, appear to be scattered over many parts of Germany, especially the skirts of the Thuringerwald, the Fichtelgebirge, the mountains of Saxony, and the Reisengebirge of Silesia. But of these the information I have been able to procure has been scanty and imperfect; topographical works on continental geology being of all others the most difficultly procurable in this country. In order however to complete this enumeration of the principal trap formations of Germany, I shall bring together such particulars as I have been able to glean respecting their characters, position, and relations. The Rhongebirge, a chain of mountains east of Fulda, appears to be a continuation of the same overlying formation, which constitutes the Vogelsgebirge, and is seen in so many other parts of Hessia. Of this district I have seen no account of more modern *See for this and other particulars a Memoir in Leonhard's Taschenbuch for 1823, by the Oberbergrath Sefb. + The Wirtemburgischer Jahrbucher for 1824, contains an account of these basalts, and an extract is given from it in the Bulletin des Sciences for November, 1825. date than that of Voigt in his work entitled " Beschreibung des Hochstifts Fuld," published in 1783. This writer speaks of the whole country as indicating volcanic action, containing in most parts rocks of basalt and clinkstone porphyry (hornschiefer). South-east of Fulda is a circular cavity which he considers to have been a crater, and which is full of water, like the Maars of the Eyfel district. It is closed in by two hills, which meet towards the east, but on their western extremity leave an aperture in which the hollow called the crater is found. The first of these hills, called the Euben, is composed of what Voigt denominates lava, probably a scoriform or amygdaloidal basalt; the second, the Pferdekopf, of porphyry slate, which seems to have been forced through the lava. The sandstone rock adjoining is hardened and otherwise altered, and where the lava is in contact with it, there is an intermixture between the two. From this account of Voigt's one should be led to conjecture, that some of the volcanic rocks of the Rhöngebirge are more recent than those of the neighbouring country, and posterior even to the formation of the vallies, but I am not aware that the statements of this Geologist have been confirmed by any more modern observer. The example indeed of Faujas St. Fond, who saw traces of craters in the basaltic rocks of the Hebrides, ought to render us cautious in receiving accounts given by geologists of this school, at a period when every volcano of whatever age was imagined to have been formed after the model of Etna and Vesuvius. Dr. Boué, in his paper on Germany, notices the passage of this clinkstone rock into a kind of pearlstone at Helsburg near Coburg. On the north-eastern limit of Bohemia at the foot of the Fichtelgebirge occurs a series of basaltic cones, extending from Egra to Parkstein. The localities are: Parkstein, where indurated marl is imbedded in the basalt, as at Eisenach; Neustadt am Culm, Kemnat, Culmain, Friedenfels, and five different spots between Waldsassen, Redwitz, and Witterstein. At Egra, the hill of Kammerberg is a conical heap of scoriæ, probably of more recent date than the basalts with which it is associated. The hot springs of Carlsbad (which, in Berzelius's opinion, owe their temperature to the rise of carbonic acid and steam, strongly heated at a great depth, through the mineral waters of the place) may perhaps be regarded as a proof that the volcanic action goes on to a certain extent even at the present time. From Egra to Toeplitz, and from thence to the Reisengebirge in Silesia, a chain of basaltic and clinkstone hills appears to extend in a direction nearly parallel to that of the primitive range of the Saxon Erzgebirge. Near Toeplitz in Bohemia basalt and clinkstone occur united, as near the Lake of Constance, the latter forming the lofty conical hill of Bilin, in which fragments of gneiss occur surrounded by the volcanic matter. Beds of tuff alternating with tertiary limestone appear in the neighbourhood. The hot springs of Toeplitz are well known. I visited this spot in 1820, but in too superficial a manner to speak with confidence with respect to the age and character of these rocks,-I believe however that they will be found to belong to the class of tertiary volcanos. Dr. Boué states in his memoir on Germany,‡ that scoriæ occur at Friedland in the Mittelgebirge, and likewise in the circle of Pilsen, at Wolfsberg, and at Salesel. A similar series of basaltic cones occurs likewise on the Saxon side of the Erzgebirge, from the neighbourhood of Schwartzenburg on the south-west, to the hill of Stolpen beyond Pirna on the north-east. || * Der Kammerberg bey Eger beschrieben, Von T. V. Goethe. Leonhard's Taschenbuch. + Berzelius in Gilbert's Annalen d. Phys. vol. 74, p. 113. The English abridgements of the memoir do not contain the remarks to which I allude. Journal de Phys. for 1822. |