58 Dr. R. D, Thomson on Hair Salt, or [July 



iron, much manganese, and one per cent lime and magnesia. 



Water extracts from it common salt, gypsum, bitter 



salt, sulphate of manganese, and a trace of sulphate of 



alumina. 



The salt itself consists of 



Magnesia 14-579 



Protoxide of manganese 3*616 

 Sulphuric acid .... 32-258 

 Water 49-243 



99-696 

 corresponding with 



11 MS. -t- m?z S. + 91 Aq. 



The rock on which the salt lies is a granular schistose 

 quartzose rock of a greenish-gray colour, with small silvery 

 scales of mica, and is impregnated with the salt matter 

 which covers partly the surface with flakes, and partly 

 incrusts it. The flocky portion consists of bitter salt, the 

 crust of alum, with a small quantity of bitter salt. The 

 rock on which the river flows is a granular gray quartz, 

 with some small scales of mica. The roof of the cave con- 

 sists of red conglomerate, in which rolled quartz occurs, 

 and occasionally pyrites and oxide of iron. The neighbour- 

 hood is formed of hills 800 feet high, which are intersected 

 by deep vallies, and capped by limestone. This limestone 

 contains small portions of carbonate of magnesia, with 

 traces of manganese and iron. Fossil oyster, and muscle 

 shells were observed on the upper part of the hill, between 

 Uitenhage and Enon. Hence, it would appear to be a very 

 recent tertiary formation. It is worthy of notice that the 

 alum and bitter salt are formed separately, and that neither 

 of them contain iron, although the oxide of that metal 

 occurs abundantly in the conglomerate. The feather alum, 

 according to Hofrath Stromeyer, is a new hitherto unde- 

 scribed species of alum, in which the sulphate of alumina 

 occurs in combination with sulphate of manganese and 

 sulphate of magnesia. Hence, he terms it mangan-magnesia 

 alum. Sulphate of manganese has never previously been 

 detected in any species of alum. 



At Tschermig, in Bohemia, an ammoniacal alum is found, 

 which, according to Lampadius and Gruner, consists of 



