34 GRANITIC ROCKS OF OTHER COUNTRIES [Oh. III. 



quartz predominating ; and it assumes various aspects, ac- 

 cording to the size of its crystalline concretions. In ascend- 

 ing the valley of the Use, about a league from Ilsenburg, bare 

 escarpments of granite present themselves, which appear to 

 belong to beds of granite situated in the midst of a different 

 kind of rock, which, being less durable, has been removed by 

 the eroding influence of existing causes. 



At Rosstrapp, on the eastern extremity of the Hartz, the 

 granite is disposed in regular beds, with a general inclination 

 towards the east; and these beds appear to alternate with 

 quartz -rock, greenstone, schist, and a variety of mica-slate. 

 On the northern side of the Hartz, at Adenberg, M. Bonnard 

 saw a bed of granite distinctly enclosed in strata of quartz- 

 rock and schistose jasper, of which the mountain is composed. 

 And on the north-western side of the Brocken, several beds 

 of granite alternate with greenstone : the latter rock is not 

 perfectly stratified, but the beds of the former clearly run 

 north and south, dipping towards the east.* 



It is difficult, however, to separate the description of the 

 granite from that of the schistose rocks by which it is 

 accompanied, when they are associated in alternating beds : 

 the details concerning the granite of Norway and the Alps 

 will be found in another Chapter. 



In concluding these brief details concerning the granitic 

 rocks, we will only observe, in addition to the remarks which 

 have been incidentally made, that a comparison of the granitic 

 formation of Cornwall with that of other countries shows, that 

 some compounds that are of rare and limited occurrence in 

 the former, are developed elsewhere into extensive masses ; as 

 in the instances of the binary compounds of quartz and mica, 

 and quartz and talc : and, vice versa., the porphyritic granites 

 and porcelainous protogine, sparingly scattered in other coun- 

 tries, are abundant in Cornwall, as are likewise, in a still 

 greater degree, the shorlaceous varieties of granite, and the 



* Annales des Mines, torn. vii. p. 44. el seq. 



