l-i OS HAUYNE-TRACHYTE AND ALLIED R0CK8. 



that of conimoii i^reen hornblende, and not Avith that of 

 avfvedsonite, ^vhich is a > ft > f. But the startling 

 opacity suggests something out of the common, and in 

 some sections the absorption varies to (l > r > H, vvhich 

 characterises the bhick alkali-iron hornblende of certain 

 phonolitic trachytes and linguaites Avhich Brogger has 

 called cata])horite. It seems to us possil)le that the horn- 

 blende is of a cataphoritic nature, though its extinction 

 angle is rather lo\\' for that species, c : o = 14° to 17°, 

 whereas in cataphorite it A'aries from 23° to G()°. 



A l)right green slightly pleochroic augite occurs in 

 prisms and grains, c : 6* = 134° or thereabouts. Apatite 

 in grains. The groundmass consists of small sanidine 

 prisms in fluxional arrangement, interspersed with, small 

 grains of augite. The whole is rather obscured by de- 

 composition. 



Tertiary haliyne-trachytes occur in France (Auvergne) ; 

 hatiyne-phonolites in Germany, Portugal, the Canaries, 

 Colorado ; the nosean-phonolite of the Wolf Rock, Corn- 

 wall, is the nearest related rock in Britain. 



Hauyne-Trachyte. 



Found on the crest of the Livingstone Hill, and in the mine tunnel l'>() 

 feet below. Also in the trench at Mount Mary Mine, west of Lovett. 



Macroi-icopicd I cli a i xictei '8. 



A soft light grey rock, easily recognised by its large 

 tabular orthoclase felspars lying thickly in parallel layers, 

 causing the rock to split more easily in that direction. 

 These felspars are mostly betAveen |" and IJ" in length, 

 and from ^" to ^' thick, and can be often chipped out 

 from the matrix, making good specimens for the ca])inet. 

 They are tabular || 010, and the cleavage parallel to this 

 plane is perfect. The crystals are opaque externallj^, light 

 yellow, but occasionally the interior is glassy, sanidine- 

 like. Mr. Frank Rutley has aptly described them to us as 

 having a biscuit-like appearance. The miners call this 

 rock " magpie." The only other pronounced macroscojjical 

 element is limonite in hexagonal and other sections after 

 some cubic mineral, probably garnet. The same rock 

 occurs at the Mount Mary Mine, where it is more decom- 

 posed, and contains miich epidote. 



Microscopical characters. 



The orthoclase is often intergrown with a striped felspar. 

 It encloses numerous hexagonal and other sections of 

 hatiyne, replaced by liebenerite (?). The rock is full of 



