46 3*1 li. J. AV. GREGORY ON THE 



thesis, and supported it by a chemical and microscopic examination 

 of the rocks ; the criticism and works of both Prof, von Zirkel and 

 Prof. Eoscnbusch were, however, wholly ignored. 



The two opposing theories had one point in common, viz. that they 

 regarded variolite as the contact-product of abasic dyke with the rocks 

 into which it is intrusive. In a paper " On the Variolitic Rocks of 

 Mont Genevre," published in this Journal *, it was shown that this, 

 the generally accepted view, did not hold for the rock in its typical 

 locality. The admirable description of M. F. Loewinson-Lessing t 

 has shown that the same is the case with the less altered variolite of 

 Yalguba. Prof. Dalmer's t descriptions of the mode of occurrence 

 of the Schonfels variolite in Saxony also suggest doubts as to the 

 applicability of the older theory to that rock, since the diabase here 

 seems to be variolitic throughout, as at Galgenberg, or at least to 

 the extent of fifty yards from the contact-plane ; this might, of 

 course, be explained as due to subsequent intrusions of diabase into 

 already consolidated masses, but there is nothing in Prof. Dalmer's 

 description to show that this has occurred. 



Such very various materials have been at different times included 

 among the variolites that it seemed quite possible that the Fichtel- 

 gebirge varieties might have had a somewhat different origin. 

 Hence it became advisable to examine some of the South-German 

 localities of the rock, and compare its mode of occurrence at these 

 with that of the Cottians and Liguria. Por this purpose the district 

 around Berneck seemed most suitable, as from it had been derived 

 the varieties of which the microscopic structure had been so care- 

 fully described by Prof. Eosenbusch, and for which Prof. Giimbel's 

 theory had been proposed. 



IT. General Features oe the Surface. 



The little town of Berneck is picturesquely situated in the mouth 

 of the valley of the Oelschnitz, at the north-east margin of the 

 Pichtelgebirge. It extends from the confluence of the Oelschnitz 

 with the Weisser Main, for about a kilometre up the deep and 

 narrow valley which the former stream has cut through the great 

 diabase massif to which this locality owes most of its geological 

 interest. The diabase appears in the map of the Bavarian Ober- 

 bergamt (Blatt Miinchberg, l^o. xi.) as covering an irregular triangle, 

 about 4 kilometres long, with a base of some 2| kilometres. The 

 area occupied by the diabase forms a high rugged plateau, divided 

 into a series of " Leite " §, on the sides of which the best sections are 

 to be seen; these are, however, never very satisfactory, as the 



* G-. A. J. Cole and J. W. Gregory, Quart. Journ. Geol. Soc. toL xhi. (1890), 

 pp. 295-332. 



t Tscb. Min. u. Petr. Mitth. vol. yI. (1884), pp. 281-300, pi. iv. ; and 

 " Olonetzkaya Diabazovaya Formatziya," Trudui St.-Peterburgskagho Obshch. 

 Estest. xviii. (1888), pp. 1()5-169. 



I Erlauterungen zur geol. Speeialkarte cles K. Sachsens. Section Planitz- 

 Ebersbrunn ; Bl. 124, pp. 25. Leipzig, 1885. 



§ This is a provincial word, meaning " place," whether plateau, slope, crest, 

 or even valley. 



