BULL. DEPT. GEOL. UNIV. CAL. 



VOL. 3, PL. 18. 



DIAGRAMATIC COMPARISON OF ANALYSES 



Spaces.. = 1 pet cent. 



Al 2 3 — Fe O + Fe. 2 3 



Ca — Mg O 



Na 2 O — K 3 O 



Percentage of Si 2 indicated by position of initial point of curve on right side 

 of triangle. 



LITH. BRIT70H t3,R£Y, S.F. 



