J. J. Harris Teall—Oheviot Andesites and Porphyrites. 2538 
less are an alteration product of the original pyroxene. Iron oxides 
are comparatively rare in thisrock. The ultimate base is a brownish 
isotropic and minutely granulated substance. Under the highest 
power at my command (1000 diameters) the granulation cannot be 
resolved, and I am therefore not able to say that any clear homo- 
geneous glass is present. Veins containing quartz and calcite occur 
in the rock. 
The Ooquet, a short distance above Blindburn.A somewhat light- 
brown rock, evidently much altered. The ground-mass appears 
compact. The porphyritic felspars are somewhat kaolinized. This 
rock is essentially similar to the last in character and composition, 
except that it was in the first instance vesicular. The vesicles are 
now occupied by an intimate mixture of quartz and chalcedony. 
Banded Porphyrite between Phillip and Blindburn.—This consists 
of alternating bands of lighter aud darker material, the darker bands 
standing out on the weathered surfaces in the form of ridges. The 
prevailing colour is a dull grey. Macroscopically the rock consists 
of a compact matrix, throughout which are scattered small por- 
phyritic felspar crystals. Microscopically, the rock is an altered 
andesite, essentially similar, as far as the distinctly recognizable 
constituents are concerned, to that described on page 152 of the 
April Number cf the Groztocican Magazine. The microscopic 
ground-mass in the thinnest sections is brownish in colour on 
account of innumerable granules and indistinct fibres; under crossed 
Nicols, a large portion of this remains persistently dark, and is there- 
fore doubtless to be referred to the microfelsit of Rosenbusch. 
Vesicular Porphyrite, Coquet, near Carl Croft.—A somewhat light- 
coloured rock with a slight purplish tint. The ground-mass is com- 
pact, and contains the usual felspar crystals. ‘The vesicles are very 
numerous and of tolerably uniform size, measuring in their longest 
diameter about one-fifth mm. They are now more or less occupied by 
silica, in the form of opal, chalcedony and quartz, a deep rich green. 
mineral, and occasionally by limonite, the latter substance apparently 
arising from the alteration of the green mineral. Microscopically, 
the rock is seen to be an altered porphyrite of the typical andesitic 
variety, and does not call for special description. The specimen is 
doubtless the vesicular portion of one of the andesitic lava flows. 
Amygdaloidal Porphyrite, Ridlees Burn, near Alwinton.—This is a 
portion of the well-known agate-bearing rock. Originally it appears 
to have been a vesicular andesite with a microlitic ground-mass. The 
cavities are now occupied by silica in its various forms, and a green 
mineral which frequently occurs in radiating fibrous aggregates, and 
gives brilliant chromatic polarization in those portions in which the 
axes of the fibres are inclined to the vibration planes of the crossed 
Nicols. The rock is also traversed by numerous irregular cracks full 
of similar products of secondary origin. The pyroxene cannot now be 
recognized in the original rock, and one may therefore conclude that 
it has supplied the material for the green alteration product which 
occurs in the amygdules. 
Rock forming crags above Langlee Ford, south side of Harthope 
