84- A DESCRIPTION OF THE [Ch. V. 



it in composition : thus, quartz-rock at Himmelsfiirst ; a com- 

 pound of felspar and tourmaline at Marienbergh; porphyry 

 at Halsbrlick ; hornblende-rock at Beschertgluck ; and lime- 

 stone in numerous places. It also envelops granite in the 

 form of irregular masses and veins, some of which are of con- 

 siderable size ; and one mass, in particular, at Geyer, is well 

 known in consequence of its having been extensively explored 

 for tin ore, in which it abounds. The gneiss of Geyers- 

 berg, which encloses this granite, is of the schistose variety, 

 and composed of the common ingredients ; the felspar, how- 

 ever, being in a less proportion than usual : its constituents 

 are not indistinctly mixed together, but are individually ar- 

 ranged in small and undulating veins. The granite is fine- 

 grained, and formed of grey quartz, brownish mica, and red- 

 dish felspar, which is always the most abundant ingredient ; 

 it contains, here and there, a little indurated lithomarge, and 

 shorl ; is a very compact sonorous rock, capable of receiving 

 a polish; occurs in beds of from two to ten feet in thickness, 

 dipping 5 to 10 towards the south-east; and is traversed by 

 numerous fissures, which intersect each other at various angles. 

 Between this granite and gneiss there is always interposed a 

 layer of some inches or feet in thickness, which is granitic, 

 but very different from that just described. It contains fel- 

 spar and quartz in pieces of two to sixteen inches in length : 

 the reddish felspar is still predominant in the mass ; the mica 

 is black in less proportion, sometimes in groups of two to six 

 inches in size ; and the quartz is often largely developed, crys- 

 talline, and compact, and in some parts in distinct pyramids, 

 forming layers which alternate with others of indurated litho- 

 marge mixed with mica. Lastly, this variety of the granitic 

 rock appears always to adhere both to the granite and the 

 gneiss on either side : indeed, these granitic and schistose 

 rocks are so intimately connected that they seem to belong to 

 the same formation. 



The gneiss of the Erzgebirge generally passes into mica- 

 slate ; so that it is often very difficult to distinguish the latter 



