242 JOSEPH P. IDDINGS AND EDWARD W. MORLEY 



phases, syenite porphyry, bostonite, and trachyte, and also phono- 

 lite, which is said to form the summit of the Pic de Maros. There 

 are varieties intermediate between shonkinite and syenite with 

 subordinate amounts of mafic minerals. A nephelite syenite from 

 the Gentungen is light gray and medium grained, with tabular 

 crystals of orthoclase and quite subordinate amounts of mafic 

 minerals. In thin section the feldspar crystals are seen to have a 

 diverse arrangement, and form the bulk of the rock, through which 

 are scattered stout hexagonal prisms of nephelite about the same 

 size as the crystals of aegirite augite, besides smaller amounts of 

 biotite and brown hornblende, also paramorphs of hornblende and 

 mica, and small crystals of sphene. The chemical composition of 

 this rock is given in analysis No. 13, which is in procenose, its 

 symbol being I. '6. (i) 2. 3. 



There are porphyritic trachytes with tabular phenocrysts of 

 glassy orthoclase, some of which are 40 mm. long and 5 mm. 

 thick. A variety with smaller phenocrysts of orthoclase, 15 mm. 

 long, has a bluish-gray aphanitic groundmass and small equant 

 phenocrysts of mafic minerals. In thin section the groundmass is 

 seen to consist of prismoids and anhedrons of orthoclase, with 

 small amounts of sodic plagioclase, nephelite, and interstitial 

 sodalite. The mafic minerals are greenish-brown hornblende 

 having very irregular outline, in part poikilitic with orthoclase 

 feldspar, also small anhedrons of green augite, and magnetite. 

 Its chemical composition is shown by analysis No. 11, pulaskose 

 I'. 5. '2. '3. Part of the normative anorthite enters the mafic 

 minerals, and part must be involved in the alkalic feldspar, which 

 must be sodic orthoclase, for no plagioclase feldspar is recognizable 

 in thin section. 



On the road from Patinoean to Tjamba, about 7 miles from 

 Patinoean, there is an exposure of altered tuff containing blocks 

 of massive, light-gray, minutely crystalline rock, with few small 

 phenocrysts of glassy tabular feldspar. Under a lens it is seen 

 to consist of subparallel tabular feldspar with abundant reddish 

 spots. In thin section the rock is seen to be holocrystalline, with 

 trachytoid fabric, composed of anhedral crystals of orthoclase, 

 yielding prismoid sections, some of which show Carlsbad twinning. 



