302 J-. W. JUDD ON THE ANCIENT VOLCANO OF 



near Heiligen Kreuz, the remains of a central cone and of a lava- 

 stream proceeding from it, the latter broken up by denudation into 

 miniature plateaux like those of the Auvergne, can be very distinctly 

 traced, as was long ago shown by Yon Pettko*. 



The basalts of the Schemnitz district exhibit some very interest- 

 ing diversities in character. In some instances, like that of the 

 well-known Calvarien Berg of Schemnitz, they contain very large 

 quantities of olivine, while in others, as, for example, the intrusive 

 mass of Gieshubl, that mineral is almost wholly wanting. The 

 latter variety constitutes a link between the true basalts and a rock 

 which is very extensively developed in Hungary, consisting of a 

 triclinic felspar, augite, and magnetite, with occasional crystals of 

 hornblende. These are the rocks now usually called augite-ande- 

 sites; but, according to Prof. Szabo, the felspathic ingredient in 

 them may be any variety of the lime-soda felspars, from andesine to 

 anorthite. In the volcanic district of the Matra, which lies to the 

 south-east of that of the Schemnitz area, the augite-anorthite rocks 

 are very extensively developed ; and hence Prof. Szabo has proposed 

 for this particular variety of the augite-andesite group the name of 

 " matraite." 



"With regard to the exact age of the basaltic rocks of the neigh- 

 bourhood of Schemnitz we have not such clear and unmistakable 

 evidence as in the cases of the andesitic and rhyolitic varieties. 

 But it is manifest that while these basaltic rocks are certainly 

 younger than the rhyolites, they must nevertheless be of consider- 

 able antiquity, seeing how greatly they have suffered from denuda- 

 tion. As wo have in other parts of Hungary, as well as Transylvania 

 and Styria, good palaeontological evidence that numerous outbursts 

 of rock of precisely similar character to the basalts of Schemnitz 

 took place during the formation of the Congerian and Inzendorf 

 beds, we can scarcely be wrong in assigning the latter volcanic rocks 

 to the same age — that is, to the older portion of the Pliocene 

 period. 



We have spoken of the outburst of the andesitic, rhyolitic, and 

 basaltic lavas of the Schemnitz area as taking place successively ; it 

 must not, however, be assumed that the production of the different 

 varieties of volcanic materials at this igneous centre can be corre- 

 lated with sharply defined and distinctly separated geological periods. 

 On the contrary, it is clear that although the great mass of the an- 

 desitic lavas was erupted before, and most of the basalts subse- 

 quently to the rhyolites, yet the three periods of eruption of dif- 

 ferent classes of rock to some extent overlapped one another. In- 

 deed at Zapolenka, near Hodritsch, we find evidence, as Yon Pettko 

 has so well shown f, that a cone and lava-stream of comparatively 

 modern date exist ; for its features can be distinctly traced. The 

 lava-stream, it is clear, must have dammed up the river-course, and 



* " G-eognostische Skizze der Gegend von Kremnitz, von Johann yon Pettko," 

 Haidinger's ' JNaturwissenschaftliche Abhandlungen,' Bd. i. (Wien, 1847) p. 302. 



t " TJeber den erloschenen Vulcan Zapolenka in der Nahe von Schemnitz, 

 von Herrn Johann von Pettko," Haidinger, Bericht vi. (1850) p. 168. 



