E. B. Tawney— Woodwardian Laboratory Notes. 453 
Microscope.—The large felspars are streaky, and show remains of 
banding, but are nearly entirely decomposed, partly to diverging 
zeolite needles, and partly to granulated similar matter; some of 
the smaller prisms show bright-coloured bands, but grey tints are 
more common. 
The augites have a tendency to collect together into grouped 
erystals, they are fresh, and polarize brightly; they contain many 
apatite prisms. There are numerous tracts of pale green viridite, 
with radiate arrangement of a fibrous structure, showing aggregate 
polarization ; some tracts are colourless zeolites in the centre, with 
similar structure, and surrounded by a viridite border. The green 
areas are also full of little spherical concretions of yellowish-brown 
matter as a nucleus, with a clear border of colourless matter showing 
aggregate polarization. Black iron oxide present is apparently titani- 
ferous. The apatite, abundant in the angite, is somewhat decom- 
posed. The rock might probably be called a Labrador-porphyry. 
The Geological Survey have not attempted to separate the felsites 
from the diabases and other igneous rocks in this district by distinct 
colours, but have occasionally placed on the map P. or F.P. for 
Felsite-porphyry, or as in this case G.P. for greenstone-porphyry. 
In Prof. Ramsay’s Memoir on N. Wales, p. 174, we read: ‘“ North 
and north-east of Pwllheli as far as Plas Du, there is a broad strip 
of rock in two places alternating with slaty bands. It hovers in 
character between a greenstone and a felspar-porphyry. At the 
trigonometrical station it consists of large crystals of felspar im- 
bedded in a hornblendic-looking base [sc]. Associated with this 
rock, about three-quarters of a mile west of Pwllheli, there occurs 
the only rock in Lleyn of an ashy or brecciated character.” The 
last statement requires a little qualification perhaps. We are not 
quite disposed to agree with the idea of the diabases passing into 
the felsites, as we saw no such passage; though they occur close 
together, they are even then quite distinct, as far as we have seen. 
The diabases seem to crop out in a series of bosses along the line 
mentioned above, are separately intrusive, and probably later than 
the felsites. 
[P. 63-68.] Labelled “varieties of trap from one mile N.W. of 
Pwllheli, near Deneio,” include two felsites and two diabases; one 
of the latter [P. 63-64] is a coarsely crystalline rock with large 
augites ; the hand-specimen shows the felspars much altered; there 
are concretions of secondary formation up to 4 inch diameter, zeolites 
and calcite, with an outer border of yellow epidote. I donot know 
the exact point from which Sedgwick collected this variety, and 
they were not sliced. These bosses seem intrusive through the 
felsite. The following one I collected in a quarry midway between 
farms of Ffrith and Henllys on the map, half a mile N. of Pwllheli; 
close by is seen the felsite. 
Diabase, N.W. of Ffrith, Deneio, in the mass shows an imperfect 
columnar structure with spheroidal exfoliation near the top of the 
quarry. A dark-green rock, which breaks frequently into flagg 
pieces, the fractured surfaces with velvety serpentinous coat; this 
