348 THE CANADIAN NATURALIST. [Vol. viH. 



Wildschapbach yielded: Si0 2 63.10, A1 2 3 20.83, MgO 0.52, 

 CaO 2.01, BaO 0.81, Na 2 9.22, K 2 2.92. 



As the feldspar, in consequence of its greater percentage of 

 lime and soda, weathers far more readily than the orthoclase of 

 the granite and moreover contains more baryta, it might cer- 

 tainly be expected that the largest veins of baryta would occur 

 in the gneiss; which is the case. Thus the vein on the Schot- 

 tenhoefen near Zell on the Harmersbach reaches a thickness of 

 25 feet, and the chief vein of the Clara Mine in the Hinterran- 

 kach near Schapbach one of forty feet. Heavyspar has played 

 an important part also in the celebrated Wenzel vein near Wit- 

 tichen. In the Friedrich-Christian and Neu Herrensegen veins 

 in Wildschapbach, which traverse granularly- banded gneiss rich 

 in the above-mentioned orthoclase, only a small part of their 

 contents still consist of heavyspar; although its former abundant 

 distribution in the vein is proved by the structure of the quartz 

 masses that carry the predominating ore (galena) and have 

 without exception retained the form of the vanished heavyspar. 

 This substitution seems to have occurred only where the feldspar 

 of the country rock has been completely changed to kaolin, i. e. 

 has been deprived of all its bases except alumina. Since con- 

 siderable quantities of silicic acid were separated out in this 

 process, as is proved by the following analyses : 



the replacement of the heavyspar is intelligible that has occurred 

 in all cases where the country-rock has not reached the utmost 

 limits of decomposition. In the gneiss there is no lack of sul- 

 phates to precipitate the baric carbonate as heavyspar. Apart 

 from my direct solution-experiments, which regularly yielded 

 scuh, Bunsen's analyses of the springs of Griesbach, Freiers- 

 bach, Petersthal and Antogast, which do not come from metallic 

 veins, as do those of Rippoldsau, but directly from the gneiss, 



