BY M. AUROUSSEAU. 303 



quartz-splinters, of extraordinary and impossible forms. The 

 interstices between the bubbles are filled with granular felspar, 

 quartz, and carbonate, in variable proportions, carbonate becom- 

 ing dominant in some patches. The interstitial material is very 

 thickly clouded with limonite-dust, which gives the rock its red 

 colour. Consolidation has evidently been brought about by the 

 introduction of quartz and carbonate. 



Texturally, the rock bears a close resemblance to the porphy- 

 roid tuff of Steimel, near Schameder, Westphalia (Lossen, 1883), 

 and to the andesitic tuff from the Old Red of Inverinan, Argyll- 

 shire (Kynaston, 1901), but differs from both in several im- 

 portant respects. 



Hudson's Peak. 



(390) Porphyritic pitchstone. — A black aphanite, with a pitch- 

 like lustre, and a very rough, subconchoidal to hackly fracture: 

 extremely brittle. 



Plagioclase, hypersthene, biotite, magnetite, zircon, and apatite 

 occur. 



The plagioclase is strongly zoned, and appears to change from 

 labradorite within to andesine without. There was one well- 

 marked change, followed by several minor oscillations. There 

 are cavities and inclusions in the outer zones. Carlsbad, albite, 

 and pericline twins occur, as well as complex aggregates. Apa- 

 tite, zircon, biotite, hypersthene, and magnetite are included. 



The hypersthene is in rounded grains, of very weak colour and 

 pleochroism, but of negative sign. It includes zircon, apatite, 

 and small felspars, and is partly moulded on, but mostly includes 

 magnetite. 



Biotite is strongly pleochroic, includes zircon and apatite, and 

 is moulded on to magnetite. 



Magnetite, zircon, and apatite are not remarkable. 



The groundmass is very strongly fluidal, consisting of alter- 

 nating streaks of yellow-brown, and colourless glass differing in 

 their refractive indices, and, seemingly, representing a residuum 

 in the act of splitting into two immiscible fractions. It contains 

 fragments of a foreign, trachytic rock. 



