On the Paragenetic Relations of Minerals. 349 



lustre than the under ones. At Nagyag (Transylvania) me- 

 tallic arsenic sits only upon the lower surfaces of rose spar. 

 3. Lodes are generally larger and richer in ore the greater 

 the depth. 4. Lodes which do not crop out can only have 

 been derived from the earth's interior. 5. Fragments of 

 rock torn from the saalbands are found above the places from 

 which they have been broken. 6. Sublimed substances must 

 have come from the interior. 7. Substances have been in- 

 troduced from the lodes into the adjoining rock, sometimes in 

 considerable masses, which appear quite foreign to it. 8. Even 

 the very frequent banded structure of lodes indicates their 

 origin from below. 



It cannot be doubted that in many instances some of the 

 constituents of minerals in lodes have been derived from the 

 surface. This is strikingly evident with regard to the phos- 

 phates, many of which are hydrated, and occur in the upper 

 parts of lodes. Pyromorphite occurs only in the upper parts 

 of galena lodes. Iu 1813, it was found, in working the Bei- 

 hilfe mine (Freiberg) close under the grass in masses of several 

 hundredweight. This mineral has in every instance origi- 

 nated from the alteration of galena. Wavellite and peganite, 

 both hydrated phosphates of alumina, occur close to the sur- 

 face in lodes in siliceous slate sandstone atZbirow (Bohemia), 

 Freiberg ; the former mineral alone at Giessen, Barnstaple, 

 St Austle, and in Tipperary. They are not known to occur 

 at any great depth. At Langenstriegis, near Freiberg, the 

 lode was purposely followed downwards for some distance, 

 and the phosphates soon disappeared; while, by working 

 along the surface, wavellite was again found, together with 

 a conglomerate of siliceous slate fragments cemented toge- 

 ther with wavellite. Herder likewise found peganite in a soft 

 state, shewing that these minerals were of very recent forma- 

 tion. It is said that there was formerly a skin yard upon 

 the spot. 



Turquoise or kalaite — consisting essentially of phosphate 

 of alumina — occurs in the East, and in Silesia and Saxony 

 only at the surface. Varizite likewise occurs in the same 

 manner. Kraurite, hydrated phosphate of iron, has been found 

 upon quartz and brown iron ore a few feet below the surface, 



