IJG TRAVELS IN BRAZIL. 



semitransparent, and with many impressions, some of them 

 very deep, one of which, measured diagonally, is nearly an 

 inch broad ; it may be asserted with the more confidence 

 that they proceed from topaz crystals, as small fragments 

 of such are still adhering to some of them. The surface of 

 this quartz crystal is rough, probably from the impressions 

 of the scaly lithomarge. Four crystals of rutile, of middling 

 size, are grown together with it. 



One rock-crystal is greyish white, at one end acumin- 

 ated with six planes, at the other, having many impressions, 

 which have been the more certainly caused by silvery 

 mother of pearl colour mica scales, as such are grown 

 together with it, not superficially only, but in the mass 

 stellarly aggregated. The other remarkable piece of rock- 

 crystal is a large fragment, with two opposite broad lateral 

 planes. The surface is partly smooth, partly with many 

 impressions, the origin of which is shown by some small 

 tables of ironglance growing together with it. On this 

 crystal, three small topazes grow superficially, and several 

 small ironglance crystals in the interior. 



For the above remarks on the topaz formation, as well 

 as for the subsequent ones, on the several formations about 

 Villa Rica, we are obliged to Chevalier V. Wagner, direc- 

 tor of mines, who has had the goodness to determine all 

 the minerals collected by us in Brazil, and to communicate 

 to us the geognostical decisions resulting from the examin- 

 ation of them, and comparisons with the mode of occurring 

 in Germany. 



