TUP. DISTRICT OF SCHEMNITZ, HTfNGABT. 317 



a greenstone-trachyte " and " dacite," and the different varieties of 

 andesitic rocks in the Schemnitz district are chemically and minera- 

 logically identical, and that their variations in structure are simply 

 the result of differences in the conditions under which they have 

 been consolidated. That the hornblende- and mica-andesites were 

 actual lavas poured out at the surface, we have the clearest proofs ; 

 and that the " greenstone- trachytes," the dacites, and the " syenite 

 and granite " constitute intrusive masses which have been forced, 

 while in a plastic and highly heated condition, through the midst of 

 the sedimentary rocks, is clearly shown by the phenomena presented 

 at the planes of contact of the two classes of rocks, and by the 

 d3'kes and veins which are seen proceeding from the one into the 

 other. 



The rocks of sedimentary origin, through which the igneous masses 

 forming the centre of the old Schemnitz volcano have forced their 

 way, have been supposed to include certain members of the Paleo- 

 zoic series ; and these rocks, which, as we have already pointed out, 

 were at first generally referred to the Primary group, have been sub- 

 sequently identified, though on very doubtful grounds, seeing that 

 thej'' contain no fossils, first as Devonian, and secondly as Dyas. 

 They are supposed to be overlain by the Triassic and Nummulitic 

 rocks of the district, which are unmistakably identified as such by 

 the fossils which they contain. 



But after a very minute and careful examination of the central 

 district of the Schemnitz volcano, I have been led to the conclusion 

 that there exists within it no series of rocks of older date than the 

 Trias, and that the supposed Palaeozoic rocks — the quartzite and 

 quartzschiefer, the crystalline and schistose limestone, and the 

 schists, gneisses, and aplite — are nothing but the arenaceous, cal- 

 careous, and argillaceous beds of the Trias, metamorphosed by their 

 contact with the Miocene intrusive masses. 



I have already enumerated the chemical and penological grounds 

 on which I have been led to infer that the rocks of granitic structure 

 in the midst of the Schemnitz volcano are identical in composition and 

 age with the surrounding andesitic lavas. There are also several 

 circumstances in connexion with the physical structure of the district 

 which lend the strongest confirmation to this view. Were the igne- 

 ous masses of Hodritsch, as is asserted, an old granitic boss upon 

 which the so-called Permian and the Triassic strata have been de- 

 posited, the conglomerates associated with these latter could scarcely 

 fail to contain pebbles of the granite and syenite. Such, however, 

 is never the case, as I can testify after a most careful examination 

 of the whole district, with a view to the determination of this point. 

 Similarly, the absence of all pebbles of the metamorphic rocks (the 

 quartzites, schists, and gneisses) of the district in the conglomerates 

 of the Trias is quite inconsistent with the view that the former were 

 in existence before the latter and constituted the basis on which 

 they were deposited. Another proof that the rock of Hodritsch is 

 not an old granite boss upon which the sedimentary rocks were un- 

 conformably deposited, is found in the circumstance that the Triassic 



z2 



