BY C. A. SUSSMILCH AND H. I. JENSKN. 181 



<001), (021), (101) and (201) are apparently best developed. 

 The crystals are optically negative, but yet almost uniaxial in 

 character. The extinction-angle on c (001) varies from 6^ to 15*^ 

 and on h (010) from 8'-^ to 10"^. Sagenitic rutile is a common 

 inclusion. Evidently this generation consists of microcline 

 cryptoperthite. The felspar of the second generation is the usual 

 anorthoclase. ^girine and augite are practically absent. 

 Strands of quartz occur interstitially. A brownish-yellow, almost 

 isotropic, titanium-mineral, surrounded by secondary leucoxene, 

 is sparingly present. It is probably perofskite. Tridymite and 

 fluorite both occur as accessories along miarolitic cavities. 

 Brown and red iron-ores, and a little chlorite and kaolin occur 

 as decomposition-products. 



Name : Trachytic Quartz-Trachyte-Porphyry, or Quartz-Solvs- 

 bergite. 



No.X.619. Trachyte-Porphyry. Loc: Dyke, Tom Cole's 

 Parm, Parish of Waldegrave, 



Handspecimen : compact, coarsely porphyritic rock. 



Microscopic texture : as in X.609. 



Composition : the constituents in order of decreasing abundance 

 Are (1) essential, felspar; (2) minor, tegirine, quartz, and magne- 

 tite, (3) accessories, zircon, fluorite; and (4) secondary, chalcedony 

 and iron-ores. The felspar phenocrjsts are twinned as in X.609. 

 The extinction-angle varies from 3° to 14°. There are two good 

 partings, and two good cleavages at about 97^^. Optically nega- 

 tive. Clearly a variety of soda-rich anorthoclase. The usual 

 inclusions are haematite, dusty garnet (?), chlorite and zircon. 

 The second generation is also anorthoclase. The pegirine occurs 

 as allotriomorphic corroded crystals, and as idiomorphic grains, 

 decomposing to chlorite and iron-ores. It is highly pleochroic, 

 and has straight extinction. In some cases a reddish-brown 

 mass of primary haematite forms the nucleus of a tufty aggregate 

 of segirine grains. In other cases a micropoikilitic aggregate of 

 haematite and felspar is seen. In such cases an original soda- 

 amphibole aggregate has probably been pseudomorphosed into 

 haematite and aegirite in the pneumatolytic period of consolidation. 



