401 



We passed between the islands of Zaruma 

 and Mina, or Mibita, covered with thick vegeta- 

 tion ; and, after having ascended the rapids of 

 the Piedra de Uinumane, we entered the Rio 

 Cassiquiare at the distance of eight miles from 

 the small fort of San Carlos. The Piedra, or 

 granitic rock which forms the little cataract, 

 attracted our attention by the number of veins 

 of quartz by which it is traversed. These veins 

 were several inches broad, and their masses 

 proved, that their date and formation were very 

 different. I saw distinctly, that, wherever they 

 crossed each other, the veins containing mica and 

 black schorl traversed and drove out of their di- 

 rection those, which contained only white quartz 

 and feldspar. According to the theory of Wer- 

 ner, the black veins were consequently of a more 

 recent formation than the white. Being a disci- 

 ple of the school of Freiberg, I could not but 

 pause with satisfaction at the rock of Uinumane, 

 to observe the same phenomena near the equator, 

 which I had so often seen in the mountains of 

 my own country. I confess, that the theory, 

 which considers the veins as clefts filled from 

 above with various substances, pleases me some- 

 what less now, than it did at that period ; but 

 these modes of intersection and driving aside, 

 observed in the stony and metallic veins, do 

 not the less merit the attention of travellers, as 

 being one of the most general and constant of 



vol. v. 2d 



