from the Pre-Camhrian of New Jersey. 



363 



when the widespread occurrence of the alkaline rocks is 

 considered. 



Table III gives the analyses of a number of these alka- 

 line orthogneisses. The examples cited belong to the 

 alkali granites, the alkali syenites, and the nepheline 

 syenites, the last named being the most numerous. The 

 Van Xest Gap rock belongs to the alkali syenites. 



Table III. 



SiO. 61.18 



AL03 . . . 



. . 16.86 



Fe.O. . . . 



. . 1.95 



FeO .... 



. . 4.74 



MgO ... 



. . 0.60 



CaO .... 



. . 2.91 



Na.,0 . . . 



. . 5.33 



K.O .... 



. . 4.12 



H.,0+ .. 



. . 0.85 



H,0— . 



. . 0.04 



TiO., .... 



. 0.61 



MnO ... 



. 0.06 



P.O, ... 



. 0.15 



CO. .... 







ZrO. ... 



. 0.16 



65.88 

 16.03 

 2.56 

 1.84 

 0.29 

 0.25 

 7.44 

 4.66 

 0.34 

 0.02 

 tr 



0.45 



3 



59.52 



21.24 



2.71 



0.48 



0.12 



0.48 



10.72 



3.92 



0.50 



tr 



tr 



0.21 



4 

 75.90 

 11.89 

 2.68 

 1.59 

 0.42 

 0.20 

 4.68 

 3.83 

 tr 

 tr 

 tr 

 tr 



5 

 63.26 

 14.84 

 2.39 

 1.54 

 4.22 

 1.61 

 9.32 

 0.70 

 1.66 



tr 



tr 



6 

 56.44 

 20.52 

 2.72 

 4.51 

 0.28 

 1.23 

 9.01 

 4.80 

 0.75 

 0.12 

 0.12 

 0.06 



7 

 55.99 

 20.18 

 4.19 

 3.25 

 0.33 

 2.29 

 6.89 

 5.59 

 0.43 



63.45 

 18.31 

 0.42 

 3.56 

 0.35 

 2.93 

 5.06 

 5.15 



0.07 



99.56 99.76 99.90 101.19 99.54 100.66 99.84 99.73 



1. Alkali quartz-syenite gneiss (akerose). Van Nest Gap, N. Y. Dr. 

 J. E. Wolff, analyst. 



2. Arfvedsonite gneiss, Cervadaes, Alemtejo, Portugal. H. Eosenbusch, 

 Elemente der Gesteinslehre, p. 620. 



3. Aegirine-nepheline gneiss. From near locality ''2". Ibid. 



4. Eiebeckite gneiss. Near Gloggnitz Austria. Ibid. 



5. Fmptekite gneiss (astochite gneiss). West Greenland, Ibid. * 



6. Canadite gneiss (miaskose). Lille Elringe, Almunge, Sweden. P. Quen- 

 sel, Bull. Geol. Inst. Upsala, vol. 12, p. 190, 1914. 



7. Nepheline-syenite gneiss (viezzenose). Makarainga, Madagascar. 

 A. Lacroix, Comptes Eendus, vol. 155, p. 1125, 1913. 



8. Augite-syenite gneiss (akerite). Loon Lake, N. Y. H. P. Gushing, 

 Bull. Geol. Soc. America, vol. 10, 179-192, 1899. 



Summary. 



1. An alkaline gneiss from the pre-Cambrian of New 

 Jersey is described with regard to its megascopic and 

 microscopic characters. 



2. Chemical analysis shows this rock to be an alkaline 

 quartz syenite gneiss belonging to the subrang akerose, 

 in the norm classification, and to the family granodiorite, 

 in the quantitative mineralogical classification of Johann- 

 sen. 



