12 ox HAUYNE-TRACHYTE AND ALLIED ROCKS. 



The augitc seems to be <lio])side, of a dirty green colour, 

 with an occasional disposition to bleach. It is in ill- 

 formed prisms, without perfect terminations. Its extinc- 

 tion angle is about -40°, and it often has perceptible 

 pleochroism. Augite grains, too, are numerous, and large 

 nests or agglomerations of granular augite occur. 



The third constituent in order of frequency is a 

 yellowish-brown biotite with strong basal cleavages, 

 showing in sections perpendicular thereto. Rays vi])rating 

 parallel to a undergo least absorption, t being opaque- 

 brown, and a yellowish-brown. There is a little apatite 

 in stout short prisms and large irregular grains. Some 

 decomposition material similar to the yellow products 

 after haliyne is present. The rock contains neither quartz 

 nor hornblende, and is altogether an unusual one. We do 

 not know of any similar occurrence with which it can be 

 compared. It appears to belong to the group of aplitic 

 dyke rocks (Rosenbusch), but the absence of aegirine and 

 the abundance of a high-angled augite shut it out from 

 the tinguaitic set. Still, we feel tolerably certain that its 

 place is in the soda-trachyte series, and among the dyke 

 rocks in that series. 



Hauyxe-Trachyte. 



Sp. gr. 2 "55. 



Occurs near the shaft on hill at Livingstone Mine, near Lovett. 



JIacroscopical characters. 



A bluish-grey porphyritic rock with crowded layers of 

 glistening tabular sanidine felspars. The smaller por- 

 phyritic elements are hornblende, augite, brilliant dark 

 garnets, and numerous soft white sections of haliyne. 

 This is the only rock which we have found with com- 

 paratively fresh or unaltered haiiyne (nosean). 



31/ c roscop ica I cli aracters. 



The felspars are clear in section. The fragments in the 

 slides are generally too imperfect for reference to par- 

 ticular zones. The orthoclase is much intergrown with, 

 oligoclase : there are fragmentary sections of Carlsbad 

 twins with albite twinning on one half, sometimes with a 

 cross striation. Partial twinning frequent in orthoclase 

 crystals, but sometimes very faintly visible. Some felspars 

 seem to have l^een enlarged by a subsequent addition of 

 material, which surrounds the original crystals as a fringe. 

 This must have taken place prior to the final consolidation 

 ^of the rock. 



