lo6 TOURMALINE-BEARING ROCKS, MT. HEEMSKIRK. 



boron, fluorine (both of these are present in tourmaline), 

 hydrogen sulphide and water -would have a very powerful 

 chemical action on the wall of the fissures, producing the 

 complete metamorphisni of the wall rock, which has already 

 been described. The more viscous quartz-tourmaline 

 magma might be erupted later and form quartz-tourma- 

 line dykes. 



It w^ill be remembered that the quartz-tourmaline veins 

 traverse both the normal granite and the tourmaline 

 granite and aplites, while in several instances the quartz- 

 tourmaline dykes were observed to fault the quartz- 

 tourmaline veins. The relative ages of all of the 

 tourmaline-bearing rocks, described in this paper appear 

 therefore to be as follows,— (1) normal granite, (2) tourma- 

 line-granite, (3) tourmaline-aplite, (4) quartz-tourmaline 

 veins, (5) quartz- tourmaline dykes. 



