24 Bulletin of Laboratories of Dcnison University [Vui. xii 



the northwest quarries of the ridge. While no distinct evidence 

 bearing on the contemporaneous origin of the tourmahne 

 aggregates in the granite with those of the pegmatite and the 

 tourmahne veinlets, it seems reasonable to assume such con- 

 temporaneity. 



The very nature of the areas oppose the hypothesis of 

 direct secretion out of the eruptive granite magma. On the 

 other hand, the characteristic mode of occurrence and intimate 

 relationship to certain other mineral species present, as shown 

 both macroscopically and microscopically, make it reasonably 

 certain that the tourmaline areas have resulted from fumaroles 

 highly charged with boric acid acting on the feldspars and mica. 



Geological Laboratory, Denison University, 

 Granville, Ohio. 



