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Show 222 MIOCENE PERIOD· [Ch. XVI. The lacustrine strata. are composed of gravel, grit, and mica-ceous san d st on e , Of Such materials as were derivable from the surrounding primary rocks; and so great is the thickness of this mass that some valleys intersect it to the depth of seven or ei()'ht ~undred feet without penetrating to the subjacent formati~ ns. In one part of the series, carbonaceous shales occur, and several seams of coal from two to six feet in thickness, hut no impressions of plants of which the species could b~ d~termined and no shells have been discovered. Many enttre Jaws and o:her bones of an extinct mammifer, called by Cuvier Anthracotherium, have been found in the coal-beds, the bone being itself changed into a kind of coal; but as this species does not occur elsewhere in association with organic remains of known date, it affords us no aid in our attempt to assign a place to the lignites of Cadi bona ~. MIOCENE VOLCANIC ROCKS. · Hungary.-M. Beudant, in his elaborate work on Hungary, describes five distinct groups of volcanic rocks, which, although rarely of great extent, form striking features in the physical geography of that country, risin~ as they do ,abruptly from extensive plains composed of tertiary strata. 1 h~y may ha~e constituted islands in the ancient sea, as Santorm and Mtlo now do in the Grecian archipelago ; and M. Beudant has remarked that the mineral products of the last-mentioned islands resemble remarkably those of the Hungarian extinct volcanos, where many of the same minerals, as opal, calcedony, resinous silex (silex resinite), pearlite, obsidian, and pitchstone abound. The Hungarian lavas are chiefly felspathic, consisting of different varieties of trachyte ; many are cellular and used as millstones; some so porous and even scoriform as to resemble those which have issued in the open air. Pumice occurs in great quantity, and there are conglomerates, or rather • The author visited Cadibona in August, 1828, in company with Mr.l\lurchison. Ch,XVI.] HUNGARY--TRANSYLVANIA--STVRIA. 223 breccias, wherein fragments of trachyte are bound together by pumiceous tuff or sometimes by silex. It is probable that these rocks were permeated by the waters of hot springs, impregnated, like the Geysers, with silica; or, in some instances perhaps, by aqueous vapours, which, like those of Lancerote, may have precipitated hydrate of silica*. By the influence of such springs or vapours the trunks and branches of trees washed down during floods, and buried in tuffs on the flanks of the mountains, may have become silicified. It is scarcely possible, says M. Beudant, to dig into any of the pumiceous deposits of these mountains without meeting with opalized wood, and sometimes entire silicified trunks of trees of great size and weight. It appears from the species of shells collected principally by M. Boue, and examined by M. Deshayes, that the fossil remains imbedded in the volcanic tuffs, and in strata alternating with them in Hungary, are of the Miocene type, and no identical, as was formerly supposed, with the fossils of the Paris basin. Transyl·vania.-The igneous rocks of the eastern part of Transylvania described by M. Boue, are probably of the same age. They cover a considerable area, and bear a close resemblance to the Hungarian lavas, being chiefly trachytic. Several large craters, containing shallow lakes like the Maars of the Eifel, are met with in some regions ; and a rent in the trachytic mountains of Budoshagy exhales hot sulphureous va~ours, which convert the trachyte into alum-stone, a change whJCh that rock has undergone at remote periods in several parts of Hungary. ~t~ria.-M~ny of the volcanic groups of this country bear a s1m1la~· relatiOn to the Styrian tertiary deposits, as do the Hunganan rocks to the marine strata of that country. The shells are found imbedded in the volcanic tuffs in such a manner as to show that they lived in the sea when the volcanic eruptions were in progress, as many of the Val di Noto lavas * See above, vol. i. chap. xxii. |