646 



HENRY S. WASHINGTON 



inserted the figures for my two analyses of the Fourche Moun- 

 tain rocks, which, although somewhat distant from Magnet Cove, 

 undoubtedly belong to the same general regional magma. To 

 render the diagrams less complicated the iron oxides are calcu- 

 lated together as (FeO). 



CaO 



Diagram i. 



It has already been explained that at Magnet Cove the 

 arrangement of rocks from center to periphery is regularly serial, 

 from basic to intermediate, i. e., from II to VI. If, therefore, 

 the analyses are plotted according to Iddings's method, using the 

 silica values for the abscissae, the diagram will represent in a 

 general way the variation of this particular magma in space. 

 This was done in my former paper' for the earlier analyses, and 

 the results of the present investigation are shown in Diagram i. 



' H. S. Washington, op. cit., p. 404. 



