176 Dr. Berger on the physical Structure 



saalbande is in general of a different nature from the substances 

 to which it is contiguous : it is sometimes composed of clay, some* 

 times of amianthus, of mica in layers, &c. It is not found in all 

 veins, and those from which it is absent are said to be adherent. 

 This is, I believe, generally the case in Cornwall. 



Vein-stones are the different stony substances wnth which the ore 

 is intermixed, and which as a whole constitute the vein. It is these 

 vein- stones which I now propose more particularly to consider. 



Werner is of opinion that In the same vein the parts of the vein- 

 stone nearest to the saalbande are the oldest, those in the middle the 

 most modern, and the intermediate parts of a middle age. But what- 

 ever may be the age of these different parts of the vein, they are all 

 necessarily posterior to the rock of the mountain in which the vein 

 occurs, and In the present case, to the granite and the grauwacke, the 

 only two formations of any extent that are met wdth in Cornwall 

 and Devonshire. 



As the same vein-stones are found in different formations of veins, 

 we must therefore admit, that the same rocks have been held in 

 solution at different periods. 



Massive quartz sometimes forms alone the greatest part of the 

 vein-stone of certain veins. This is the case at Kithill near Calling- 

 ton : 1 believe that here the quartz is united to the granite without 

 any saalbande intervening. 



In the tin mines between St. Just and Cape Cornwall, quartz is 

 united with black, massive, and radiated tourmaline. The quartz 

 (exists not only in the form of veins, but also in blocks. According 

 to Bergman, there is in the mountain of Nasa, a block of quartz 

 several hundred yards broad, and double that dimension in length.* 



* Journal dcs Mines, No. xvi. p. 41. 



