Ch.XVI.] HUNGARY- — TRANSYLVANIA — STYRIA. 
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 
tuff's 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 
I trees of great size and weight. 
It appears from the species of shells collected principally by 
M. Bou6, and examined by M. Deshayes, that the fossil re- 
mains 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. 
Transylvania. — 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 
vapours, which convert the trachyte into alum-stone, a change 
which that rock has undergone at remote periods in several 
parts of Hungary. 
Styria. — Many of the volcanic groups of this country bear 
a similar relation to the Styrian tertiary deposits, as do the 
Hungarian rocks to the marine strata of that country. The 
shells are found imbedded in the volcanic tuff's 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. 
