204 TRAVELS IN BRAZIL. 



Eschwege's itacolumite, on account of its texture, stratifi- 

 cation, bed, and formation, should be called quartz-slate, 

 in analogy with other rocks of a slaty structure, or, if 

 we will not expressly indicate the texture, quartz-rock ; 

 whereby we cannot suppress the remark, that the topaz, 

 beryl, shorl, and horn rocks, may the more properly be 

 classed with this formation as the topaz, beryl, shorl, &c., 

 may be considered as not essential parts, as in other rocks 

 in which they are found. 



We had long since written our ideas on the occurrence 

 of the elastic quartz, when we received the second number 

 of the accounts of the Austrian naturalists inBrazil, and Baron 

 Von Humboldt's Geognostical Essay on the Superposition of 

 Rocks in both Hemispheres. We were rejoiced to see in 

 the former (p. 81.) that Dr. Pohl called the elastic quartz 

 likewise quartz-slate ; but his opinion that this rock is of 

 recent formation, and doubtless of alluvial origin, agrees 

 even less than the supposition before brought forward by 

 Mr, Von Eschwege, that it is sandstone, with the true 

 relative age of it, so that we presume that our respected 

 fellow-traveller has already corrected his opinion. We 

 have found the opinion of Baron Von Humboldt entirely 

 coincident, and confirming our own, for (p. 94. of the Ger- 

 man edition) he directly classes it as quartz-rock. We 

 caimot but feel highly obliged to this great geologist for 

 having by his determination thi-own light upon this subject. 



Note 6. 



The clay-slate which we remarked in the mine of Mr. 

 Von Eschwege, is of a cream-colour, inclining to brownish 

 yellow, and consists merely of small scales of mica, which 

 are soft to the touch, and easily crumble. This is probably 

 Mr. Von Eschwege's transition into talc-slate, to which, 

 however, it does not belong, but rather to mica-slate. This 



