222 MIOCENE PERIOD. [Ch. XVI. 



The lacustrine strata are composed of gravel, grit, and mica- 

 ceous sandstone, 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 eight hundred feet without penetrating to the subjacent for- 

 mations. In one part of the series, carbonaceous shales occur, 

 and several seams of coal from two to six feet in thickness, but 

 no impressions of plants of which the species could be deter- 

 mined, and no shells have been discovered. Many entire jaws 

 and other bones of an extinct mammifer, called by Cuvier An- 

 thracotherium, 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 Cadibona *. 



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, 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 archipelago; and M. Beudant has re- 

 marked 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.Murchison. 



