202 



TRAVELS IN BRAZIL. 



subordinate in it. A similar modification of granite occurs 

 also in Brazil, namely, in the Serra do Mar, in the province 

 of S. Paulo (according to Varnhagen's observation in 

 Eschwege's Journal, vol. ii. p. 241.), and in several places of 

 the capitania of Bahia. 



Note 5. 



The quartzy, granular mica-slate, elastic quartz, flexible 

 sandstone, or quartz-slate of the Morro de Villa Rica, 

 consists of a greyish and reddish white, not unfrequently 

 smoky grey, fine and very fine-grained quartz ; and of a 

 silvery white, more or less dark, pearl-grey, seldom pinch- 

 beck-brown, very delicate scaly mica, which is sometimes 

 tinged red by oxyde of iron on the rifts. The quartz 

 sometimes loses its granular structure, and forms narrow 

 strata of compact splintery fracture ; in the same manner 

 the silvery mica often accumulates on the rifts in undu- 

 lating strata, often half an inch thick, and has in that case 

 a remarkable mother of pearl lustre. Mr. Von Eschwege 

 (Gemalde, p. 17.) says of this mica-slate, that it is com- 

 posed of quartz, talc, and chlorite, of slaty structure, but in 

 a geognostical view is different from mica-slate, and as 

 such deserved to be classed as a separate kind of rock, 

 which he calls Itacolumite, After an accurate examination of 

 a great number of pieces of very different colours, which 

 are preserved as well in the Brazilian museum at Munich, 

 as in other collections, we are entitled to conclude that this 

 rock neither belongs to the sandstone, where Mr. Esch- 

 wege classed it in his earlier publications, nor consists, 

 besides quartz, of talc and chlorite; for we have never 

 observed the latter ingredients. The supposed talc is 

 merely a modified mica, which contains nothing less than a 

 predominant talc-earth, and what are called chlorite scales are 

 partly silvery, partly pearl-grey mica scales, which are some- 

 times tinged red by oxyde of iron. We have not observed. 



