116 
G. T. PRIOR. 
Under II., for comparison, is appended the analysis of a phonolite from Mont 
Miaune, Velay, France.* 
More closely approaching phonolites are rocks from the debris-heaps at Minna 
Bluff (613) and from Black Island (530). 
Specimen 613 from the Minna Bluff is a dark greenish-brown compact rock 
showing no phenocrysts. Under the microscope are seen feathery flakes of pale- 
green gegirine-augite, and ragged tufts of cossyrite and of a brown altered mineral 
(probably another soda-hornblende or pyroxene). These are thickly and uniformly 
distributed in a rather unindividualised base, showing indistinct felspar-laths and 
a few magnetite-grains ; nepheline is probably present in the base, but could 
not be definitely identified. The segirine-augite shows extinctions up to 37°, and 
pleochroism from pale grass-green for vibrations along the length to pale pinkish- 
yellow for those across the length. The cossyrite has pleochroism from nearly 
colourless to deep purplish-brown or opaque ; the shreds were too irregular to admit 
of a more precise determination of the optical characters. 
The rock (530) from Black Island is nearly colourless. Under the microscope it 
shows ( see Plate VIII, Fig. 5) a fine-grained trachytic felt of felspar-laths, with much 
deep-blue riebeckite-like hornblende scattered in minute shreds through the section, 
and accumulated in patches round small altered crystals of what was once probably 
nepheline. The riebeckite shows pleochroism from pale-brown to colourless across 
the length of fibres to indigo-blue along the length. These two rocks are similar 
to some of the phonolitic rocks of the Rift Valley, East Africa. I 
Of phonolitic rocks closely related to the kenytes two specimens deserve mention, 
viz., a rolled pebble (25) from the beach at Cape Adare, and a dark-green compact 
rock (622) from Minna Bluff (debris- heap). 
The pebble from Cape Adare is a dark-green compact phonolite showing numerous 
porphyritic felspars having the characteristic lozenge-shape of anorthoclase. Under the 
microscope, besides the large (up to 1 cm. in length) phenocrysts of anorthoclase 
showing minute twin-striations, are seen a few small phenocrysts of deep reddish-brown 
hornblende, and more numerous pseudomorphs, after hornblende, consisting of grains of 
magnetite and deejngreen aegirine-augite. The ground-mass consists of numerous 
shreds and small prismatic crystals of segirine-augite, like that in the hornblende- 
pscudomorphs, evenly distributed in a base of felspar-laths (not sharply defined) and 
interstitial nepheline. Magnetite-grains occur very sparingly in the base. A few 
small crystals of sphene are also present. 
Of somewhat similar composition is the dark -green phonolitic rock (622) from the 
Minna Bluff. It shows under the microscope numerous long prismatic phenocrysts of 
orthoclase and anorthoclase in a very fine-grained base consisting of a mesh of minute 
felspar-needles with globulites and microlites of green segirine-augite. Small crystals 
* Emmons, On some Phonolites from Velay and the Westerwald. Dissertation, Leipzig, 1874. 
t Prior, Mineralogical Magazine, 1903, vol. xiii, p. 237. 
