they trend inland, and are succeeded by secondary hills, The Alps, which may be said to expire on the side of Italy, appear rather to be continued as to their geological constitution in the primitive chains of Corsica and Sardinia, situated directly opposite the termination of the Maritime Alps against the coast, and in the line of their prolongation. From the Gulf of Genoa, the Alps pursue their course first to the NNW, through Piedmont and Savoy ; then turning suddenly to the E through Swisserland, the Tyrol, and Stiria. The primitive and transition chains have together an average breadth of between 50 and 60 miles. These are succeeded by exterior zones of limestone, principally coeval with the magnesian limestone and oolitic series, the carboniferous series being apparently absent,* or at most of very limited occurrence. The beds of the Alpine rocks where these are stratified are generally vertical ; the bordering chains exhibit marks of the greatest disturbance, their strata being contorted and dislocated. Thus on the north all the recent calcareous chains appear to dip towards, instead of rising against, the central and primitive ridges. The three following sections taken from Ebel will give a general idea of the distribution of the older rocks in the Swiss portion of the Alps : 1. Over the Bonhomme and Mount Cenis. (the Bonhomme), the Isere. Cenis). 2. Over Great St. Bernhard. . Mr. de la Roche has, however, noticed traces of the coal formation in the Col. de opps denly mitir: ho Primitive limestone. 3. Over St. Gothard. 1 1 Entry -fthe cal Ence, orth Sead Tree ad the According to Ebel's map, the transition formations, greywacke, greywacke slate, and transition limestone, form a band of small comparative extent on the north of the Alps, the rest of the chain being primitive; but, according to D’Aubuisson, Mr. Brochant considers much of the gneiss, micaslate, and serpentine, of the Alpine chains, as truly belonging to the transition series : the details are given in the subjoined note.* * M. Brochant, Professeur de Minéralogie et de Géologie à l'Ecole des Mines, alors établie à Moutiers, dans la Tarentaise, en observant divers points de cette contrée, fut frappé de la multitude de brèches et de poudingues qui s'y trouvaient; il vit les roches ces montagnes alterner avec ces poudingues, et avec un terrain anthraciteux contenant des empreintes végétales. Il exposaces faits dans un mémoire qu'il publia en 1808, et dans lequel on nous montra, pour la première fois, des schistes-micacés, des serpentines, des quartz en roche et des calcaires grenus, hors de la classe des terrains primitifs, et postérieurs à l'existence des êtres organisés. Ce mémoire classique et fondamental, pour employer les expressions de M. de Buch, fait époque dans cette partie de la science." " M. Brochant a poursuivi, dans les Alpes qui avoisinent la Tarentaise, les conquêtes qu'il venait de faire aux formations intermédiares, et il ne s'est arrêté que devant le Mont-Blanc et les Grandes-Alpes, retenu par un reste de considération pour leur ancienne prérogative de primordialité, et par cette élévation qui les place au premier rang parmi les montagnes de l'Europe : mais sans désespérer qu'un jour de nouvelles découvertes ou de nouvelles analogies ne les fissent passer dans les terrains intermédiares; et en remarquant formellement que lors même que ces hautes Alpes appartiendraient aux terrains primitifs, elles n'étaient séparées, par aucune interruption, du terrain intermédiare de la Savoie, et qu'il y avait continuité entre la formation de ces deux terrains : conclusion très-importante, et sur laquelle nous avons déjà insisté. " Je remarquerai ici que lorsqu'en 1807, M. Brochant fit le mémoire dont les consé. quences ont été adoptées par tous les minéralogistes, ce savant manquait encore d'une partie des preuves qui les rendent aujourd'hui incontestables ; alors on n'avait pas encore trouvé des coquilles dans les calcaires de la Tarentaise: Depuis les observations de M. de Brochant, dit M. de Buch, je commence à croire In this map also a double zone of primitive limestone is represented pursuing its course with undeviating regularity on either side the axis of the chain. In the Tyrol, the secondary limestones encroach more on the primitive chains, which, though still of considerable height, are tame in their features, and are more than rivalled in elevation, and far surpassed in grandeur, by the colitic rànges. The steepest escarpment of the Alps is uniformly towards the Bohemer Wald, the Thuringer Wald, the Erzegebirge, the The central line of the Alps may, perhaps, be considered as prolonged by the primitive chain, which passes from Presburg to join the Carpathians ;. but on the NW of this line is a vast group of ancient chains, extending between Vienna and Dresden, completely enclosing the sources of the Elbe, or the great basin of Bohemia, and thus forming, as it were, a detached ring in front of the general system. The Bohemer Wald, or branches connected with it, closes this basin on the SW and SE, ranging round the sources of the Elbe. On the NW border, clayslate alternating, with greenstone rocks prevails ; but in the rest of the chain, granitic rocks predominate. The Fichtelgeberge connects this side of the Boherner Wald with the Thuringer Wald : it exhibits granitic summits skirted by clayslate and greenstone. The slate district is very extensive on the N. The Thuringerwald (a branch extending from the NW of this primitive circle) exhibits granite, gneiss, and micaslate, skirted on the S by the overlying deposits of rothe todteliegende and cupriferous slaty limestone (our new red conglomerate, and magnesian limestone series). On the N, porphyritic rocks overlying those of the coal formation occur. Mas the BIO Hari que le gneis même, entre Martigny et Saint-Maurice, que tous les singuliers poudingues de la vallée de Trient jusqu'à Valorsine, que les rochers de gneis entre Martigny et SaintBranchiez, appartiennent au terrain de grauwacke, et ne sont pas primitifs. Ces roches se retrouvent dans tout le Valais, quoique sans poudingues.” The slate of Glaris, containing fish and turtles, which has sometimes been considered as transition, appears rather to belong to the secondary rocks. I am desirous to avail myself of this opportunity to correct an error I have inadver. tently committed in quoting a statement of Dr. Mac Culloch's on a subject nearly connected with this. In noticing his discovery of a calcareous formation containing organic remains underlying the gneiss, I have hastily used the term gryphite limestone, but the fossils observed were really orthoceratites: the whole sentence is also expressed too generally, and without sufficient precision. Instead of the brief clause sa gryphite limestone underlying gneiss in one of the Hebrides," I ought to have written " a limestone formation underlying gneiss in Garvagh, the most northerly of the Hebrides, and in the shores of Loch Eribol on the adjoining main land, which at Eribol contains a subordinate bed of calcareous sandstone, exhibiting traces of orthoceratites.” The Doctor has little doubt that the associated beds of the limestone will also be found to contain similar remains both at Eribol and in Garragh Island, haud The Erzegeberge (forming the NW border of the Bohemian basin) presents the same primitive rocks skirted by the transition series. Its ridge supports in many places insulated basaltic . summits, which are also abundant on the Bohemian side, where in the Mittelwald between the Erzegeberge and the Eger, they repose on tertiary deposits containing lignite. Porphyritic rocks overlying coal abound on the N of this chain as in the Thuringerwald. The Riesengeberge (a continuation of the Erzegeberge on the opposite side of the Elbe, forming the north-eastern border of the Bohemian basin) has a central granitic axis, skirted by gneiss sometimes including micaslate, by clayslate, and lastly, by transition rocks; The gneissy zone is most extensive on the north, and that of clayslate on the south, of the central range. Beyond the valley of the Neisse, the continuation of this chain (here principally composed of clayslate), assumes the name of the Sudetengeberge, and ranging round the district of Glatz, unites itself with the slaty ridges proceeding from the Bohemerwald, thus completing the enclosure of the Bohemian basin (which, as we shall hereafter see, is occupied by the carboniferous series, new red sandstone, tertiary, and basaltie formations). · The Valley of the Oder on the north, and of Moravia on the south, separate these chains from those of the prolongation of Alps towards the Carpathians ranging by Presburg (L.) Carpathian Mountains. These mountains range in a semicircle round Hungary from Presburg, on the W, to the neighbourhood of Belgrade on the E; the ancient rocks, however, are not exhibited on the surface throughout the whole of this semicircle, there being an interval near the middle of its course (above the sources of the river Theiss) in which the older rocks only appear in patches bursting through an overlying sandstone deposit. With this exception, however, which does not amount to more than a sixth part of the whole semicircular range, the older formations are uninterrupted. They present first a central granite, then granite, gneiss, and micaslate, alternating together. 3. Micaslate and clayslate containing granular limestone. 4. Serpentine diallage rock (Euphotide) and greenstone porphyry. 5. Transition rocks. Having enclosed Transylvania by a rapid bend, the primitive chain crosses the Danube below Belgrade. It then appears to extend itself to the S, turning round to the E, and forming the chain of the Balkan or Mount Hæmus. (M.) Mount Balkan or Hamus. I am not acquainted with any geological description of this chain. Macmichael, however, observes, in crossing it from a 1 be a pro 24 Gablova to Shipka, that the strata on the N are generally calca- may longation of this chain. (N.) The Range of Caucasus. This, though beyond the limits of Europe, is necessarily included in our present survey, being placed exactly on the prolongation of the line of Mount Balkan, and of the slaty tract of the Crimea, of which it, therefore, appears to be the continuation, forming with it the southern border of the great European basin. It is said to exhibit the usual primitive and transition rocks skirted by compact limestone, and to exhibit near its centre some overlying summits of floetz trap. (O.) Granite Plains of the Dnieper. These appear to constitute a group of primitive rocks protruding through the secondary and tertiary deposits of the great basin: granite principally prevails, and the country is characterised by the unusual circumstance, that although of primitive structure, it is yet low, and, except where furrowed by the valleys of the rivers traversing it, level. (P.) The Ural Chain. The great European basin is open through a wide interval, destitute of any primitive barrier towards the Caspian and Aral. Whether any primitive zone exists behind these inland seas, or how far the secondary deposits extend in this direction into Asia, is unknown; but on the NE, the Ural Mountains on the confines of Europe and Asia again present a primitive border, exhibiting, according to Pallas, the usual central and collateral zones of ancient mountain chains. It seems probable, but has not, I believe, been ascertained, that the primitive rocks of Finland on the north of the great basin extend along the shores of the White Sea till they join the northern extremity of the Ural chain, thus completing the primitive margin of the basin on that side. (To be continued.) |