SUMMARY AND CONCLUSIONS 33 1 



averages roughly 20 per cent and is appreciably higher than in the other 

 analyses. Iron oxides and magnesia are low in I, III, and IV, but are 

 correspondingly high in the other four (II, V, VI, and VII), with a 

 similar variation noted in lime, a difference which results from the dis- 

 tribution in amount of mafic silicate minerals in the two groups of rocks. 

 Ferrous iron and magnesia combined dominate total lime, being approxi- 

 mately equal in several cases. The total alkalies are usually high, with 

 the range in soda from low to very high, and potash generally high, but 

 very low in IV. Soda without exception molecularly exceeds potash. 



Chemical Analyses of igneous Dike Rocks from Middle Western Virginia 



I II III IV V VI VII 



Si0 2 69.56 57.62 54.77 53.57 48.10 43.26 40.40 



1.159 .960 .912 .892 .802 .721 .673 



APO 3 . . .' 15.52 16.44 21.41 22.46 15.25 14.01 13.49 



.152 .161 .210 .221 .150 .137 .132 



Fe 2 3 1.67 2.34 2.46 1.01 2.57 7.17 5.87 



.011 .014 .016 .006 .016 .045 .037 



FeO 1.19 4.89 0.68 0.92 8.28 5.41 4.88 



.017 .068 .010 .013 .115 .075 .068 



MgO 0.41 2.53 0.18 0.37 9.33 5.57 8.01 



.010 .064 .004 .009 .233 .139 .200 



CaO 1.20 6.40 0.47 1.49 11.11 10.09 10.02 



.021 .114 .009 .027 .198 .180 .179 



Na 2 4.46 2.91 9.53 10.22 1.48 2.83 3.45 



.073 .047 .153 .165 .024 .045 .056 



K 2 4.68 1.52 4.97 5.14 0.35 3.78 2.94 



.050 .016 .053 .054 .006 .040 .031 



H 2 0— 0.34 0.20 0.17 0.43 0.53 0.49 0.61 



H 2 0+ 0.67 1.15 4.61 2.97 1.22 2.74 3.06 



Ti0 2 0.31 0.64 0.08 0.20 0.69 1.81 2.21 



.004 .008 .001 .003 .009 .02:5 .028 



P 2 5 0.08 0.29 0.07 0.11 0.11 1.18 1.09 



.001 .002 .001 .001 .001 .008 .008 



MnO 0.07 0.27 0.68 0.56 0.15 0.3 1 0.63 



.001 .004 .010 .008 .003 .005 .008 



BaO 0.10 



.001 



C0 2 None 3.75 0.03 0.95 0.83 1.57 3.72 



.020 .018 .036 .oni 



S Trace None 0.17 0.20 0.21 0.19 



.006 .006 .one. .our, 



100.26 100.95 100.11 100.57 100.20 KM). 10 100.57 



l. Felsophyre from Monterey Mountain, Highland County, Virginia. W. i 

 Hillebrand, analyst. 



XXIII— Hulk. GboL. Soc. Am., Vol. 24, 1912 



