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acids, though silex and alumine predominate* 

 in them : they are strongly impregnated with 

 carbon, and sometimes blacken the hands, like 

 a real vitriolic schistus. The pretended gold 

 mine of Cuchivano, which was the object of our 

 examination, is nothing but an excavation cut 

 into one of those black strata of marl, which 

 contain pyrites in abundance. The excavation is 

 on the right bank of the river Juagua ; and must 

 be approached with caution, because the torrent 

 there is more than eight feet deep. The sul- 

 phurous pyrites are found, some massive, and 



where there is no muriatiferous gypsum, between the slaty 

 sandstone with roestones (bunte sandstein, Wern.) and the con- 

 glomerate or ancient sandstone. It contains strata of schis- 

 tous and coppery marl (bituminoce mergel and kupferschieferj 

 which form an important object in the working of mines at 

 Mansfeld, in Saxony, near Riegelsdorf, in Hesse, and at Ha- 

 sel and Praunitz, in Silesia. In the southern part of Ba- 

 varia (Oberbaiern), I saw the alpine limestone, containing 

 these same strata of schistous clay and marl, which, though 

 thinner, whiter, and particularly more frequent, character- 

 ize the limestone of Jura. Respecting the slates of Blat- 

 tenberg, in the Canton of Glaris, which some mineralogists, 

 because of their numerous impressions of fish, have long 

 mistaken for the cuprous slates of Mansfeld, they belong, 

 according to Mr. Von Buch, to a real transition formation. 

 The whole of these geological data tend to prove, that strata 

 of marl, more or less mixed with carbon, are to be found in 

 the limestone of Jura, in the alpine limestone, and in the 

 transition schists. The mixture of carbon, sulphuretted 

 iron, and copper, appears to me to augment with the relative 

 antiquity of the formations. 



