583 



EEPORT OF NATIONAL MUSEUM, 1890. 



II. 



Silica 



Alumina 



Iron sesquioxide , 

 Iron protoxide ... 



Magnesia 



Lime 



Soda 



Potash 



Water 



Specific gravity . 



Per cent. 



4G. 9 3 



21.59 



8.09 



2.49 

 7.97 

 8.93 

 2.04 

 2.09 



Per cent. 



42.37 

 8.88 



11.26 

 7.80 



13.01 



10.93 

 4.51 

 1.21 

 0.34 

 3.103 



Colors.— The prevailing colors are various shades of gray to nearly 

 black. 



Structure. — Structurally they are porphyritic with a holocrystalline 

 or in part amorphous base, usually fine grained and compact, at times 

 amygdaloid al. 



Classification and nomenclature. — These rocks differ from the basalts, 

 which they otherwise greatly resemble, in that they bear the mineral 

 nepheline in place of feldspar. Based upon the presence or absence 

 of olivine we have, first, Neplmline basalt, and second, Nephelinite. 

 The name Nepheline dolerite has been given in gome cases to the coarser 

 holocrystalline olivine-bearing varieties. 



Like the leucite rocks the rocks of this group are somewhat limited 

 in their distribution. They are at present represented iu the collection 

 as follows : 



Nephelinite : Herchenberg and Hahnenbacher Ley, Ehenish Prussia, 36550 and 36551 ; 

 Monte Vulture, near Melfi, Italy (Hauynopuyr, so called because ricb in the 

 mineral Hauyn), 56552, 73012, and 73010 ; Neudorf, Saxony (Hauynbasalt), 

 36548. 



Nepheline basalt : Near Weiler, Baden, 35861 ; Katzenbuckel, in tbe Odenwald, Ba- 

 den, 36557 and 73040; Eppstein, in the Taunus Mountains, Germany, 36555; 

 Rossberg, near Rossdorf, Hesse, Germany, 36558 ; Hydrotachylite iu same, 36502 ; 

 Spechtshausen, Saxouy (transitional variety, near Limburgite), Loban, Saxony, 

 36553 ; Salzberg, near Schlau, Bohemia (noseauite of Boricky), 36549 ; Kletschner 

 Berg, Bohemia, 36554 ; Scheibenberg, in the Erz-Geberge, 36559. 



15. The melilite rocks. 



Professor Rosenbusch places under this head a small group of rocks 

 heretofore known as melilite basalts, in which the mineral melilite is 

 the chief constituent, with accessory augite, olivine, nepheline, biotite 

 magnetite, perowskite, and spinell. The normal structure is holo- 

 crystalline porphyritic, in which the olivine, augite, mica, or occasion- 

 ally the melilite, appear as porphyritic constituents. 



These are rocks of very limited distribution, and at present repre- 

 sented in the Museum collections only by specimens from Wartenberg, 

 Bohemia, and from near Owen, in Wurtemberg (35860 and 36577.) 



