369 



and from Gorlitz in Silesia, this mineral is one of the most 

 important constituents. He proposes that these rocks should be termed 

 melilite-basalts. Olivine and melilite are the principal constituents of 

 these rocks. Augite also occurs, but plays a less important part than 

 either of the other constituents. Olivine and a part of the augite 

 occur as porphyritic constituents. The ground-mass is essentially com- 

 posed of the remainder of the augite and of melilite. Nepheline, mica, 

 magnetite and perowskite occur as important accessories. Apatite and 

 hauyn occur sparingly. The rocks are extremely basic in composition 

 and from 92 to 95 per cent, is soluble in hydrochloric acid with separa- 

 tion of gelatinous silica. BORICKY'S " nepheline-picrite " belongs to this 

 group, so that BORICKY'S term is inappropriate. 



I. II. 



Si0 2 ... 33-89 ... 27-52 



Ti0 2 ... 0-64 ... 2-67 



A1 2 3 ... 9-93 ... 9-48 



Fe 2 3 ... 15-63 ... 13-37 



MgO ... 16-14 ... 16-64 



CaO ... 15-19 ... 16-75 

 K 2 



Na 2 ... 2-86 ... 2-38 



PA ... 1-41 ... 1-19 



CO ... 1-41 ... 6-36 



H 9 2-90 3-27 



100-00 99-68 



I. Melilite-basalt. Hochbohl near Owen. Swabian Alps. STELZNEB. N.J. Beilage 

 Band 1882, p. 398. Rock contains also traces of manganese, chromium and sulphur 

 II. Melilite-basalt. Devin. Bohemia. Analysis by BOEICKY. Quoted from STELZNEE'S 

 paper. The rock contains also 0'27 CrzOs and '10 S. 



The distinguishing chemical characteristic of the leucite- and nepheline- 

 bearing rocks is the high percentage of alkalies. Now there are other 

 rocks which resemble them in this respect, but differ in containing neither 

 of these minerals. To this group belong the keratophyres of the Fichtel- 

 gebirge and the Hartz, the rhomben- porphyry of southern Norway, the 

 pantellarite of the island of Pantellaria, between Sicily and Tunis, and 

 some of the augite-syenites. The most striking mineralogical feature 

 of these rocks is the occurrence in all of them of felspars of exceptional 

 composition, and sometimes also, as in the case of the rhomben-porphyry, 

 of exceptional form. The name, keratophyre, was introduced by GDMBEL 

 for certain rocks associated with the Cambrian strata (Phycoden-schiefer) 

 of the Fichtelgebirge. (1) These rocks are according to him of variable 



(1) Die palaolithischen Eruptivgesteine des Fichtelgebirges, p. 43. 



