Quartz and Metalliferous Veins. 131 



the fluid circulating in the vein-fissure through as naiTOW an 

 interstice as between two staves. As in the example ad- 

 duced, copper was deposited at first by a chemical process, 

 and afterwards by an efffect of contact, so, in like manner, 

 substances might be deposited from fluids cii'culating in vein- 

 fissures. Though no such energetic chemical affinities oc- 

 curred in the latter, as between the iron and the sulphate of 

 copper, time might compensate for deficiency in energy of 

 affinity. 



The impregnation of the adjacent rock with ores belongs 

 exactly to this category. This impregnation of the vv^alls, as 

 well as of fragments in the vein, is generally strongest 

 where the adjacent rock is at the same time very much de- 

 composed, or interpenetrated by extraneous matter. The 

 minutest impregnation with tin-ore runs through most tin- 

 vein formations, chiefly so far as the adjacent rock is silicified 

 at the same time ; and there are tin " courses" {zuge) whose 

 " strings" have scarcely any tin-bearing vein-stuff's, — merely 

 barren clefts, which are worked solely for the sake of the 

 impregnated adjacent rock. Alongside many veins of the Frey- 

 berg lead-formation, blende and galena appear here and 

 there to form the striated component of the gneiss, in place 

 of felspar and mica. Yet much more frequent in the Frey- 

 berg lead-veins is the impregnation of the gneiss in and ad- 

 jacent to them with arsenical and ii'on pyrites. The adja- 

 cent rock has also been worked here and there, on account 

 of its impi'egnation with the richer silver ores. The impreg- 

 nation does not always correspond exactly with the ore-pro- 

 duce of the vein in the same place. Thus there presents 

 itself, in a certain vein, only quartz, with parcels of iron- 

 pyrites and galena ; whilst the adjacent rock, so far as dis- 

 closed, is strongly interpenetrated by large granules of black 

 blende. Impregnation with arsenical pyrites is often met 

 with near Freyberg galena veins, at points where they can'y 

 very little or no arsenical pyrites, &c. 



All these appearances have this in common, that the ad- 

 jacent rock is much decomposed, or interpenetrated by extra- 

 neous ingredients in the locality of the impregnation. Both 

 indicate an exchange between the components of the adja- 



