Thelianz. 109 



Granite. 



This rock makes its appearance at two distinct and isolated points, 

 as may be seen in the profile. They are situated in the western 

 part of the range, and being the most elevated points, occasion the 

 rapid descent, already remarked upon in speaking of the torrents. 

 This rock as it appears at the Brocken and the Rostrapp respectively, 

 differs essentially in the state of aggregation, and consequently in phys- 

 ical aspect. Felspar is the principal constituent of the granite of the 

 former, and those points which have been long exposed to the air, 

 are of easy decomposition, giving a rounded, graceful form to the 

 summit of this mountain, resembling that of mount Jefferson one of the 

 peaks of the White Mountains in Nev^ Hampshire. This granite is 

 of a reddish hue and often so resembles sienite as to deceive the ob- 

 server. The crystals of tourmaline found here are well terminated 

 but of small dimensions. The Rosstrapp is by far the most romantic 

 spot in the Hartz, differing from the Brocken, from which it is sepa- 

 rated by the argillaceous schist and transition limestone. Quartz 

 forms the most abundant ingredient of this granite ; unsusceptible of 

 decomposition, its primitive rough exterior has resisted the inroads 

 usually caused by the dilapidations of time, presenting its natural 

 form, giving a harshness to the environs equalling the granite scenery 

 of Switzerland. An isolated rock forms the limits of the granite 

 formation, it is situated in the valley of Isenthal and has received 

 the name of Iselstein; this rock is of granite and of large dimen- 

 sions possessing a singular and remarkable peculiarity, that of mag- 

 netic polarity, the cause is inherent in the mass ; the fragments do 

 not alter the course of the needle. 



The granite of the Rosstrapp contains irregular veins of greenstone, 

 which appears to be of a posterior formation ; the point of contact 

 of these two rocks is compact, whereas the mass is of a strong 

 crystalline structure ; this effect might have been produced by the 

 melted greenstone filling the crevices of the granite not yet solidified 

 or the greenstone might owe its formation to the absence of alkali, 

 which might have been replaced by magnesia at the moment of for- 

 mation ; like circumstances having existed, it would be natural to 

 suppose, that the passage between the two rocks would be insensi- 

 ble. It contains nodules of quartz, and occasionally garnets ; am- 

 pliibole becoming abundant the rock becomes very crystalline ; some- 

 times it contains crystals of felspar and becomes porphyritic. The 



