894 THE GEOLOGY OF THE NANDEWAR MOUNTAINS, 



only as occasional grains, and in the presence of a little inter- 

 stitial quartz {cp. Tables i. and ii.). 



N.31. Loc: base of Ningadhun Rock. 



Handspecimen : a dark porphyritic rock showing felspar 

 phenocrysts in an aphanitic base. It was taken within a few 

 feet of N.30 and N.25, but belongs to a totally different flow. 



Texture apparently holocrystalline, the isotropic patches being 

 referable to analcite and other decomposition-products; por- 

 phyritic, and with cryptocrystalline tomicrocrystalline pilotaxitic 

 base which may be partly de vitrified glass. 



Composition : the phenocrysts are corroded and partially 

 resorbed at the edges, and consist of andesine. A brownish- 

 green hornblende has been present in the form of phenocrysts, 

 but is now almost wholly replaced by chlorite, secondary magnetite 

 and haematite. The groundmass consists of microlites of ande- 

 sine, isotropic or almost isotropic decomposition-products and 

 nepheline, a few stunted rods of a colourless pyroxene, acicular 

 crystals of a yellow pyroxene which may be a relative of wohlerite, 

 magnetite and minute cubes of green spinel (pleonaste). A 

 number of decomposition-products are present, amongst which 

 the chief seem to be haematite, chlorite and dusty magnetite after 

 hornblende and pyroxene; and sericite after felspar; also natrolite 

 and opal infilling vesicles. 



Name : Phonolitic Andesite. 



N.49. Loc: slopes of Mount Ningadhun. (Plate li., fig. 3). 



Handspecimen reddish-brown in colour, very hard, and aphanitic. 



Texture apparently holocrystalline, microcrystalline to crypto- 

 crystalline base, with phenocrysts; trachytic fabric. 



Composition : the main constituents are microlites of orthoclase 

 and albite, nepheline in corroded phenocrysts whose resorbed 

 edges show alteration to cancrinite and geisikite, a highly 

 pleochroic brown hornblende, probably cossyrite, with haematite 

 and magnetite and sphene as decomposition-products, needles of 

 a brown pyroxene not unlike wohlerite, and glass. The rock is 

 amygdaloidal, the infillings of the vesicles consisting of zeolites 

 and opal. 



