Ch. XXXI.] HUNGARIAN VOLCANOES. 683 



We may easily conceive that a similar mass might now be pro 

 duced, if a copious evolution of gases should occur in one of the 

 lake-basins. The water might remain for weeks in a state of violent 

 ebullition, until it became of the consistency of mud, just as the sea 

 continued to be charged with red mud round Graham's Island, in the 

 Mediterranean, in the year 1831. If a breach should then be made 

 in the side of the cone, the flood would sweep away great heaps of 

 ejected fragments of shale and sandstone, which would-be borne 

 down into the adjoining valleys. Forests might be torn by such 

 a flood, and thus the occurrence of the numerous trunks of trees dis- 

 persed irregularly through the trass, can be explained. 



The manner in which this trass conforms to the shape of the pres- 

 ent valleys implies its comparatively modern origin, probably not 

 dating farther back than the Post-pliocene, or, at farthest, the jSTewer 

 Pliocene period. Of like modern date are numerous perfect cones 

 of scoriae and some streams of lava which occur in the Eifel, as, for 

 example, the small cones with craters near Andernach, on the left 

 bank of the Ehine, and the columnar lava of Bertrich-Baclen, be- 

 tween Treves and Coblentz, of which I have given a figure at p. 619. 



Hungary. — M. Beudant, in his elaborate work on Hungary, de- 

 scribes five distinct groups of volcanic rocks, which, although no- 

 where of great extent, form striking features in the physical geogra- 

 phy of that country, rising as they do abruptly from extensive plains 

 composed of tertiary strata. They may have constituted islands in 

 the ancient sea, as Santorin and Milo now do in the Grecian Archi- 

 pelago ; and M. Beudant has remarked that the mineral products of 

 the last-mentioned islands resemble remarkably those of the Hunga- 

 rian extinct volcanoes, where many of the same minerals, as opal, 

 chalcedony, resinous silex {silex resinite), pearlite, obsidian, and pitch- 

 stone 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 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 in- 

 stances, perhaps by aqueous vapors, which, like those of Lancerote, 

 may have precipitated hydrate of silica. 



By the influence of such springs or vapors the trunks and branches 

 of trees washed down during floods, and buried in tuffs on the flanks 

 of the mountains, are supposed to have become silicified. It is 

 scarcely possible, says M. Beudant, to dig into any of the pumiceous 

 deposits of these mountains without meetiug with opalized wood, 

 and sometimes entire silicified trunks of trees of great size and 

 weio-ht. 



