TRANSLATIONS AND NOTICES 



GEOLOGICAL MEMOIRS. 



On the Gneiss and Granite o/* Central Bohemia. 



By M. JOKELY. 



* [Proceed. Imp. Geol. Instit. Vienna, March 13, 1855.] 



During the summer of 1854, M. Jokely examined the gneiss and 

 granite mountains around Millotitz in Central Bohemia. The gneiss 

 occurs only at the southern extremity of the district in question, and 

 forms the extreme northern termination of the gneissic group of 

 Southern Bohemia. It constitutes an elevated plateau of slightl}'- 

 undulating country, only in a few localities attaining more than the 

 average altitude of 1500 feet. The strike of the gneiss corresponds 

 with the boundary-line of this formation ; the dip is between N. and 

 W., so that it plunges everywhere beneath the granite. 



The most conspicuous rock subordinate to this gneiss is granite in 

 the form of beds or veins. The granite beds, lying conformably with 

 the gneiss, are connected with veins and masses of auriferous and 

 argentiferous quartzites, formerly the object of mining enterprise. 



Granulite and amphibolic slates appear locally. Patches of ter- 

 tiary sand, clay, and gravel, overlying the gneiss, at altitudes of as 

 much as 1400 feet, occupy a larger extent of surface. These deposits 

 were once connected with the tertiary freshwater basin of Wittingau, 

 at the N.W. extremity of which they form a bay. 



Alluvial deposits and kaolin, resulting from the decomposition of 

 granitic rocks, are the most recent formations within the district 

 under notice. 



The granite prevails within the district ; its surface is highly undu- 

 latiag ; the average elevation is 1800 feet; some isolated cones attain 

 a height of 2500 feet. The chief varieties of the granite are granitic 

 gneiss, more or less fine-grained true granite, micaceous granite, and 

 porphyritic granite, which as they nearly everywhere contain par- 

 ticles of amphibole, may also be called amphibolic granites. 



Subordinate to the granite are granites in beds or in veins with 

 quartzites, and amphibolites with diorites and porphyries. The 

 stratiform granites, lithologically identical with the fine-grained light- 

 coloured granites of the gneiss, are especially frequent in the eastern 

 portion of the district ; iheir strike is between N.E. and E., and 



VOL. XII. — PART II. C 



