MODE VII. SAUSSURITB. 355 



verging towards the green, from an excess of 

 magnesia. 



This stone may be regarded as intermediate 

 between basaltin and serpentine, and might be 

 called magnesian basaltin ; but as it is the most 

 remarkable pier re dc corns of Saussure, it has 

 been thought proper to give the name of that 

 great observer to this important rock. 



The pierre de corne* or corneenne, is a vague 

 appellation, still retained by the French mine- 

 ralogists. It sometimes implies a trap, some- 

 times a wacken, sometimes an earthy siderite ; 

 and sometimes more appropriately the present 

 rock. Saussure has observed, 1225, that when 

 the corneenne appears crystallised, it assumes 

 the name of hornblende. He has given, 725, 

 an analysis of his pierre de corne, and observes, 

 that the chief difference between it and basalt 

 is the mixture of magnesia. In Kennedy's ac- 

 curate analysis of basalt there is no trace of 

 magnesia ; but in the Saussurite there ought to 

 be more than 6 in the 100. The decomposition 

 of the iron often forms a kind of bark around 

 this stone, whence it has been called by some 

 authors pierre-a-ecorce. 



Dolomieu, in his celebrated memoir on felsite 

 and trap, which precedes his distribution of vol- 

 canic products, observes, that the cavities in 



2 A 2 



