Ch. V.] PRIMARY SCHISTOSE ROCKS. 85 



from the former, at the point of transition. The mica-slate 

 varies much in colour, and in composition ; and it is only 

 in a few places, that it exhibits its distinguishing character 

 of interlaminated quartz and mica : when this happens, it 

 abounds in disseminated garnets. This slate contains some 

 subordinate beds of quartz-rock, of hornblende-rock, and of 

 compounds in which garnets and actynolite are very abundant. 

 It is generally succeeded by argillaceous schist, into which it 

 may be seen to pass at Schneeberg. 



The clay-slate also sometimes reposes immediately on the 

 gneiss, as at Joachimsthal ; where, likewise, it may be seen 

 passing into hornblende-schist. At Johann-georgenstadt, 

 this rock even comes in contact with the granite ; but in this 

 position, it is always of an intermediate nature, between mica- 

 slate and clay-slate, and contains layers of quartz-rock. 



But the most rare and interesting rock, in the primary 

 schists of the Erzgebirge, occurs at Auersberg, and was first 

 described by Freiesleben. It is composed of quartz and shorl, 

 as mica-slate is of quartz and mica ; and it has, therefore, 

 been called shorl-schist : it also occasionally contains mica, 

 chlorite, garnet, and other minerals ; but these are not essen- 

 tial. Its structure is striped or ribboned, formed by alter- 

 nate layers of quartz, and fibrous or granular shorl : the 

 stripes are seldom straight, but for the most part variously 

 curved and undulating. The shorl-schist reposes on the 

 granite : and, although this rock has been only seen in situ 

 at Auersberg, there is every reason to believe that it exists 

 elsewhere ; since pebbles of it are often found in the alluvial 

 deposits which contain tin ore : and its presence may be 

 regarded as a favourable indication of this metal, as it has 

 hitherto always occurred associated therewith.* 



Before concluding the description of the primary schistose 

 rocks, it will be desirable to consider a little more in detail 

 the series in which talc is the characteristic mineral over 



* Annales des Mines, tomes 8 et 9. 

 G 3 



