xii 



have traversed the most uncultivated parts 

 of Europe. Our progress was often re- 

 tarded by the threefold necessity of drag- 

 ging after us, during expeditions of five or 

 six months, twelve, fifteen, and sometimes 

 more than twenty loaded mules, exchang- 

 ing these animals every eight or ten days, 

 and superintending the Indians who were 

 employed in leading so numerous a cara- 

 van. Often, in order to add to our col- 

 lections of new mineral substances*, we 



* The mineral and vegetable substances which we 

 have brought from America, several of which were 

 till then unknown, have been submitted to chemical 

 analysis by M. M. Vauquelin, Klaproth, Descotils, 

 Allen, and Drapier, who have given descriptions of 

 them in separate memoirs. I shall here mention two 

 new mineral species : The feuer-opal, or quartz resi- 

 nite mielle of Mexico (Klaproth, chem. Unters. der 

 Min. T. iv, p. 156. Sonneschmidt Beschr. der Mex. 

 Bergref. S 1 19. Karsten min. Tabellen, 1808, p. 26, 

 88.) and the conchoidal muriated silver of Peru, 

 muschliches hornerz (Klapr, IF, 10. Karst, p. 60, 97. 

 Magazin der BerL "Naturf. I, 158) ; the silver ore, pa- 

 co of Pasco {Klapr. IF.) the antimonial gray copper ore, 

 graugultigerz of Tasco (Kl. If, 74.) ; the mete- 

 oric iron, meteoreisen, of Durango, (Kl. IF, 101); 

 the ferriferous carbonated limestone, staenglicher 

 braunspath, of Guanaxuato, the crystals of which 

 reunited in bars form equilateral triangles (KL IF, 



