NORITE 229 



even in parts of a single section, but it is remarkably fresh. Ilmenite is 

 developed in scattered irregular granular masses of large sizes, partially 

 altered to leucoxene. Both primary and secondary quartz occur contain- 

 ing abundant inclusions of rutile needles. Original hornblende was not 

 identified in any thin section of the rock. 



CHEMICAL COMPOSITION AND CLASSIFICATION 



The composition of the Blue Ridge gabbros described above is shown 

 in analyses I and III of the subjoined table. Ill shows no unusual 

 features in composition, but I is especially interesting because of its un- 

 usual richness in Ti0 2 and P 2 5 . It is compared with the analysis (II) 

 of the new rock type gabbro-nelsonite of the near-by Amherst-Nelson 

 comagmatic area. The two rocks are rich, but not equally so in Ti0 2 

 and P 2 5 . In most other respects the two rocks are chemically unlike, 

 as indicated not only by the analyses, but by their positions in the quanti- 

 tative system, I being a salfemane and II a dofemane. Mineralogically, 

 however, the two are closely similar, since they contain the same silicate 

 and ore minerals, but in different proportions. 



For purposes of comparison, analyses of hypersthene gabbros (norites) 

 from several well known eastern areas are introduced in the table — IV 

 and V from the Amherst-Nelson, Virginia, area ; VI from the Baltimore, 

 Maryland, area, and VII and VIII from the Adirondack region. Disre- 

 garding the gabbro-nelsonite represented by analysis II, the rocks show 

 decidedly close chemical relationships, as indicated by their positions in 

 the quantitative system. They are all salfemanes and fall into order I 

 or 5, rang 3 or 4, and subrang 3 or 4. 



Analyses of Gabbros 



I II 43 



Si0 2 42.10 33.83 



A1 2 3 12.06 5.19 



Fe 2 G 3 1.10 11.38 



FeO 8.43 15.08 



MgO 5.62 8.57 



CaO S.63 8.22 



Na 2 1.97 1.28 



K,0 1.12 .50 



H 2 0— 20 .45 



H 2 0+ 3.80 .75 



Ti0 2 10.15 4.84 



P 2 5 3.77 10.00 



MnO 63 .26 



43 Contains C1-- - .04, F — .55. 



Ill 



IV 



V 



VI 



VII 



VIII 



47.67 



50.99 



51.08 



46.85 



47.16 



44.77 



15.93 



12.40 



16.45 



19.75 



14.45 



12.46 



1.96 



2.10 



.84 



3.22 



1.61 



4.63 



6.80 



11.80 



10. OS 



7.99 



13.81 



12.99 



8.99 



4.09 



6.95 



7.75 



5.24 



5.34 



12.32 



6.46 



5.57 



13.10 



8.13 



10.20 



1.68 



2.38 



3.49 



1.56 



3.09 



2.47 



.79 



2.19 



1.28 



.09 



1.20 



.95 



.12 



.12 



.08 



}. 56{ 



.12 



.12 



1.80 



1.21 



.51 



.48 



.48 



.85 



4.66 



4.44 





3.37 



5.26 



.13 



1.S6 



.14 





.57 



.28 



1.51 



.11 



.08 





.24 



.17 



