Geology of the Harz Mountains. 235 



6. Metamorphic Eocks. 



a. Contact Metamorphism. 



The granites and the intrusive diabases of the Lower Harz 

 are surrounded by a fringe of more or less highly meta- 

 morphosed strata. The contact metamorphism has been 

 carefully studied by various investigators, including Lessen, 

 who has, at different times, given elaborate accounts of it 

 in the " Zeitschrift der deutschen geologischen Gesellschaft." 

 The compact diabases which generally occur in large beds 

 are accompanied by " green shales " (griine Schiefer), i.e., 

 micaceous chloritic shales with hematite scales, quartz, 

 granular calcite, plagioclase, and siskin green epidote, either 

 mixed with the rock or in strings and veins. The shales 

 occur, as a rule, either above or below the Hauptkieselschiefer, 

 but rarely in that rock itself. Ferruginous quartz, probably 

 a decomposition product of the green chloritic mineral, and 

 of the red ironstone to be afterwards noticed, occur along 

 with the compact diabases. 



The green shales are best developed in a band surrounding 

 the diabase patches, between Stiege and Eodishayn, a village 

 situated about 5 kilometers S.W. from Stolberg. 



The contact rocks of the granular diabase gabbro are quite 

 different from the green shales just described as occurring 

 around the compact diabase. They are essentially divisible 

 into two groups (1.) Kieselschiefer, (2.) " Band- " and 

 " Fleckschiefer " or " Desmosit " and " Spilosit." 



(1.) These siliceous shales really belong to a totally dif- 

 ferent family from the true kieselschiefer, whose acquaint- 

 ance we have already made. They are intensely hard, have 

 a flat conchoidal fracture, are very compact and splintery, 

 and generally grey in colour, but are sometimes banded, 

 and although very difficult to fuse, can, by a good blast, be 

 converted into a whitish slaggy enamel. They have been 

 classed as halleflinta by Naumann, of whose nomenclature 

 Lessen approves. The adinoles which occur at Lerbach on 

 the Upper Harz are quite analogous to the halleflintas — 

 indeed, with the exception of the greater fusibility of the 

 former, there appears to be no difference between them. The 



