FOYAITE-IJOLITE SERIES OF MAGNET COVE 



667 



this secondary differentiate is a product it is a little difficult to 

 say, but the evidence of Williams's descriptions, my own obser- 

 vations, and the mineralogical and chemical data, indicate that 

 it was the foyaite sub-magna (VI) which has undergone this 

 further change. 



If this view be correct there must exist a complementary 

 differentiate, a rock in which the positions of the various oxides 

 are, as regards the "normal" curves, inverse to those of covite. 

 That is, the loci of silica, alumina, and the alkalis would be 

 above, and those of iron oxides, magnesia, and lime would be 

 below, the "normal." 



Whether we actually find this rock or not is more or less an 

 accidental matter of erosion, etc. But a chemical analysis indi- 

 cates that such exists in the case of the "foyaite" which 

 occupies the small area in the northeastern part of the main 

 mass, which was erroneously colored as ijolite on Williams's 

 map.' This is a white, coarse-grained, holocrystalline rock. 



SiOo 



AI063 



Fe;03 



FeO 



MgO 



CaO 



NagO 



KoO 



HoO (iio' + )... 

 H^O (iio^-)... 



C62 



TiOo 



P2O; 



Other constituents 



53-54 

 23-95 

 I . II 

 1.24 

 0.08 

 0.71 

 8.62 

 8.87 

 1 .09 

 0. 14 

 0.20 

 trace 



99-55 



53-09 

 21 . 16 

 1.89 

 2.04 

 0.32 

 3-30 

 6.86 

 8.42 



I-I3 

 0.24 

 0.82 

 0. II 

 0.15 

 0.95 



100.48 



III 



49.70 

 18.45 

 3-39 

 4-32 

 2.32 

 7.91 

 5-33 

 4-95 

 1 .09 

 0.25 

 none 



I 33 

 0.40 



99-44 



IV 



53-11 

 23.62 

 1.36 

 1-47 

 0.33 

 I-5I 

 8.25 



8-43 



1.82 



892 



234 

 007 

 017 

 002 

 012 



139 

 094 



I. Foyaite, nortlieast part of area. 

 II. Foyaite, Diamond Jo quarry. 



III. Covite, schoolliouse, western part of area. 



IV. Mixture of eiglit parts of I, and one of III. 

 la. Molecular ratios of I. 



^ Cy. H. S. Washington, op. cil., p. 394, note. 



