18 ON HAUYNE-TRACHYTE AND ALLIED ROCKS. 



llcwroscop ica I cli aracters. 

 A compact greenish grey rock, with large isolated glis- 

 tening tabular crystals of sanidine. Numerous small 

 black garnets embedded in the rock, and dark augite 

 prisms visible under hand-lens. 



Microscopical cJiaracters. 



The large sanidine crystals are clear and fresh-looking. 

 Dodecahedi-al sections of brown-zoned garnet in simple 

 and compound forms enclose prisms of augite. These 

 large garnets are a feature in the rock slice. Green 

 pleochroic augite in imperfect forms of the prism occurs 

 in nests. The extinction angle is as high as 37°, and the 

 mineral often encloses crystals of apatite, a yellowish 

 green, i) yellowish, t green. Some sphene is present 

 porphyritically. A little pale yellowish brown biotite is 

 associated with the nests of augite crystals. It can be 

 picked out in the slide by its strong pleochroism — a yel- 

 lowish brown, c opaque. 



The groundmass consists of small lath-shaped sections 

 of sanidine with fluxional arrangement and pale green 

 pleochroic rods of aegirine extinguishing parallel to their 

 length. Granules and small crystals of sphene are plen- 

 tiful. There is some isotropic material of a zeolitic 

 nature. 



Melanite-Trachyte. 



Stones of this rock were found at the back of Widow 

 Cleary's cottage on the road to Cradoc, about 2 miles N.W. 

 ■ of Lovett, at the foot of the green conical hill which rises 

 there from the road. The hill exposes permo-carbon- 

 iferous mudstones a few hundred feet up, with abundant 

 marine fossils. This is the most northerly extension of 

 the trachyte which we examined, but we could not find it 

 in situ. 



Macroscopica I characters. 

 Light brown in colour, granular in texture, studded 

 with brilliant black crystals of melanite-garnet. This 

 mineral is such a constant and abundant accessory that the 

 rock may well be called a melanite-trachyte. 



Mineral constituents. 



Orthoclase, perthite, melanite, augite, apatite, biotite, 

 sphene, analcime, chlorite, limonite (manganese .?). 



Microscopical characters. 

 The most frequent porphyritic element is melanite- 

 garnet, light and yellowish-brown, in thin section, in the 



