8 J. Tf. Judd — On Volcanos. 



Now, it is quite inconceivable that a glacier, whicli had sufficient 

 excavating power to produce that great depression in the solid rocks 

 among which Lake Balaton lies, could, nevertheless, have left stand- 

 ing right in its course such a mass of comparatively soft tuffs as 

 constitutes the peninsula of Tihany. And it must therefore be clear 

 to every one that, unless the volcanic outbursts which formed this 

 mass can be shown to be of later date than the Glacial Epoch, the 

 basin of Lake Balaton could not possibly have had its origin in ice- 

 action during that period. 



But concerning the geological age of the tuffs of Tihany we have 

 the most unmistakable evidence in the fossils which they contain. 

 These prove conclusively that the volcanic outbursts by which they 

 were formed took place during the deposition of the ' Congeria 

 Schichten ' — which are placed by Karl Mayer on approximately the 

 same horizon as our Coralline Crag. That the basaltic lavas and 

 tuffs of the Bakony Wald were formed long prior to the Glacial 

 Period there is not, indeed, the slightest room for doubting ; and 

 this conclusion is quite in harmony with the appearances of very 

 extensive denudation which these volcanic rocks present ; — the lava- 

 streams being reduced to isolated plateaux, the tuffs in great part 

 swept away, and the plugs of basalt, that have filled the throats of 

 the old volcanos, in many cases left standing above the rocks they 

 have penetrated. 



Dismissing then on these conclusive grounds the theory of glacier- 

 erosion, as certainly inapplicable to the case of Lake Balaton, let us 

 inquire if the examination of the district does not suggest any 

 other mode of origin for it. Such, we think, every geologist will 

 at once recognize as indicated by the volcanic outbursts that have 

 taken place, not only on its northern and southern shores, but also 

 in the midst of its bed. The volcanic district of the Bakony Wald 

 and Lake Balaton, which is illustrated in our sketch-map, Plate L 

 (the materials of which are derived from the Geological Maps of the 

 Vienna Eeichsanstalt and those of the Geological Institute of Hun- 

 gary), is a portion only of a linear series of later Tertiary volcanos, 

 which stretches south-westward from the Matra of Northern Hun- 

 gary to the Danube, being produced on the opposite side of that river 

 by the trachytic outbursts lying north-east of Stuhlweissenburg, 

 and beyond the Bakony Wald in the opposite direction through 

 Styria to the neighbourhood of Gleichenberg. It is impossible to 

 doubt that the peculiar arrangement of this series of contem- 

 poraneous volcanic outbursts points to the existence of a line of 

 fissure in the earth's crust at the time of their occurrence ; and it is 

 a very significant circumstance that the longer axis of the great 

 depression in which Lake Balaton lies exactly coincides with this 

 line of volcanic action. 



We have already had occasion to refer in these chapters to the 

 local subsidence which, as demonstrated by Darwin, so frequently 

 follows the cessation or accompanies the decline of volcanic activity 

 in a district ; and which is so admirably illustrated by the Lipari 

 Islands and Santorin among recent volcanos, and by that of Mull 



