172 



TRAVELS IN BRAZIL. 



earth, produced by the decomposition of this chlorite-slate, 

 or fine white sand, but in a greasy mica, modified into Utho- 

 marge, which may be called scaly lithomarge, and in friable 

 lithomarge, partly pure and partly mixed with much red 

 ochre, which is accompanied with quartz and porcelain 

 earth. Mawe has comprehended both the varieties, under 

 the name of soft earthy talc, for which' they certainly may 

 be taken. 



Mr. Von Eschwege himself has adduced the most solid 

 reasons against the assertion of a secondary repository. 

 On such a supposition we must assume a flotz chlorite- 

 slate, and even regularly stratified ; besides, we do not find 

 the matrix from which the topazes may have been detached ; 

 neither is it to be conceived how, under such circumstances, 

 they could be enveloped in the lithomarge, as in an original 

 repository. We may add, that this is the more difficult to be 

 explained, when we consider that both on the topazes and 

 euklase evident impressions of very fine scales of lithomarge 

 are to be seen, which may seem sufficiently to prove the 

 simultaneous formation. 



Lastly, if we must absolutely explain the origin of so many 

 fragments of topazes, euklase, and quartz, the hypothesis of 

 Mr. Zinken appears to be the most probable, according to 

 which, these minerals have been formed in their original 

 repository, but that a subsequent inundation penetrating into 

 the friable mass of mica, loosened it, and hereupon the little 

 cavities which arose at the formation of the separate crystals, 

 collapsed, and fractured the crystals of topaz and euklase, 

 which always have innumerable rents and fissures. Be- 

 sides the occurrence of the topazes in the scaly and crumbly 

 lithomarge, which evidently owes its origin to mica, has a 

 great analogy with the origin of the emerald in mica, or 

 mica-slate, in the valley of Heubach, in the principality of 

 Saltzburgh. 



Mr. Frischholtz says, in Baron Von Moll's new Annals, 

 vol. iv. No. 3., " That mica, separates from the gneiss. 



