18 ox HAUYNE-TRACHYTE AND ALLIED ROCKS. 



Macroscopii'dl clidrarters;. 



A compact greenish grey rock, with large isohited glis- 

 tening tabular crystals of sanidine. Numerous small 

 black garnets eml)edded in the rock, and dark augite 

 prisms visil)le under hand-lens. 



Jlicroscop ica I cha ractet 's. 



The large sanidine crystals are clear and fresh-looking. 

 Dodecahedral 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, h yellowish, c green. Some sphene is present 

 porphyritically. A little pale yellowish brown 1)iotite is 

 associated with the nests of augite crystals. It can be 

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

 lowish brown, t opaque. 



The groundmass consists of small lath-shaped sections 

 of sanidine with fiuxional 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 hundi*ed 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. 



Macruscoincal 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 "i). 



Microscopical characters. 



The most frequent porphyritic element is melanite- 

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



