HYPERSTHENE OCCURS IN MAGNESIA N DIABASES. 347 



a diabase rich in magnesia (13.05 per cent.). It will be interesting to deter- 

 mine whether such a relationship exists between the mineral and chemical 

 composition of all the diabases of the Atlantic border. 



In the above paper the chemical work is by W. G. Brown, the petro- 

 graphical work by H. D. Campbell, and the conclusions by both. 



Washington and Lee University, 



Lexington, Va., December, 1890. 



Ll— BuLi- Geol. Soc. Am., Vol. 2, 



