306 J. W. JUDD ON THE ANCIENT VOLCANO OE 



voted especial attention to the Schemnitz area ; and the conclusions 

 at which he arrived may be briefly stated as follows : — 



Beudant seems to have regarded the outer girdle of andesitic 

 rocks as being formed synchronously with the whole " Secondary 

 series," while the syenite and greenstone of the central area he 

 referred to the earlier " Transition period," and the metamorphic 

 rocks of the same tract to the Primary. The rhyolitic and basaltic 

 rocks he justly classed, in part at least, as Tertiary, although, 

 through his unfortunate but not unnatural mistake of confounding 

 the Pliocene Congeria-heds with the Eocene Calcaire grossier, he 

 threw the whole too far back in time. The one point which all the 

 earlier geological interpretations of the district appear to have had 

 in common was the separation of the gneiss, granite, syenite, and 

 diorite, which were classed as Primary and Transition rocks, from 

 the trachytic and basaltic, which were grouped with the Secondary 

 and Tertiary. 



The more accurate study of the Tertiary faunas and floras, which 

 was initiated by the labours of Lyell and Deshayes in "Western 

 Europe, and has been so admirably extended to the east of Europe 

 by Homes, Suess, Yon Hauer, Euchs, and others, soon, however, 

 led to the recognition of the fact that all the volcanic rocks of the 

 Schemnitz area belong to the Tertiary period, and even to the latter 

 half of it. Thus there was brought about a wide separation of the 

 supposed ancient crystalline " granites, syenites, and diorites " 

 from the evidently modern " trachytes." 



But, at the same time, petrologists began to recognize the circum- 

 stance that the so-called old greenstones or diorites of the district 

 not only presented the most remarkable points of resemblance to 

 the Tertiary trachytes or andesites by which they were surrounded 

 on all sides, but that in many instances the most perfect transition 

 of the one rock into the other could be clearly traced. As early as 

 1848 we find Yon Pettko* (to whose labours, next to those of Beu- 

 dant, we are most indebted for the elucidation of the structure of 

 the complicated Schemnitz area) making the declaration that " there 

 is nothing to show that the greenstone of this district is older than 

 the associated trachyte, while the frequent transition of the two 

 rocks into each other, and their common local disposition, forming 

 together the great ring-shaped mountain-ridge, decidedly point to 

 their synchronous formation." 



As this conviction of the intimate connexion existing between the 

 Hungarian trachytes and the so-called diorites became more firmly 

 established in the minds of geologists, the latter rocks acquired the 

 name of " greenstone-trachytes." This view of the relations of the 

 two classes of rocks was in part adopted by Bichthofen, when, in 

 1860f, he made his general survey of the Hungarian volcanic rock- 

 masses ; and at a later date this author suggested, as we have already 



* Berichte oiber die Mittheilungen von Freunden der Naturwissenschaften in 

 Wien, Ed. iii. 



t " Studien aus den ungarisch-siebenburgiscken Trachytgebirgen," Jahrbuch 

 der k.-k. Keichsanstalt Wien, Ed. xi. S. 153. 



