70 EE. B. Tawney— Woodwardian Laboratory Notes. 
Ascending Carn Neddol, the rock is here Orthoclase-felsite, the 
ground being paler and rather closer in texture. There is an irre- 
gular columnar appearance in the rock produced by cross joints at 
small intervals. A thin slice under the microscope shows that the 
black spots 2-3 mm. across are coloured by viridite and ferruginous 
material, and represent perhaps pyroxene ; no cleavage, etc., is how- 
ever preserved. The felspar is orthoclase, and is more or less 
minutely streaky, as if permeated by another felspar not extinguish- 
ing at the same time. One small quartz crystal in the slice. The 
ground is microfelsitic for the most part, but in places is micro- 
crystalline with some imperfect spherulites. 
At the village called Pig Street, near Llanbedrog, is a quarry, of 
which the rock looks like a coarse tuff (ash) made up of felsite frag- 
ments. These fragments are of different colours, their outlines stand 
out quite sharply in places; they seem all of the same type of rock, 
but of redder colour, while the paste contains scattered felspars, etc., 
so as to have much the same appearance as the included fragments. 
An exposure of the rock a few score of paces away shows merely 
scattered included portions of different colour, and may perhaps 
not belong to this tuff. A thin slice from the quarry near the old 
windmill, Pig Street, confirms the conclusions drawn from the in- 
spection of the rock in situ. Some of the included fragments look 
like porphyrite of dark red colour, others are felsite containing 
spherulites ; the fragments of felspar are often triclinic, and are sur- 
rounded by dark red ground, almost opaque, from colouring by iron 
oxides, and serving to make the outlines of the fragments very dis- 
tinct. This is not the only case in Lleyn of ash, as bedded ash has 
been .already mentioned at Pwllheli by Sir A. C. Ramsay, in the 
Survey Memoir on N. Wales [p. 207, ed. 2]. 
The southern point on the sea-coast at Foxhall, Llanbedrog, is 
a pale grey orthoclase-felsite, with dull white felspars about 4 mm. 
diameter, with ochry centres due to decomposition [Sedgw. Coll. p. 
107]. The microscope shows a micropegmatitic structure very 
prevalent in in the ground; the minute quartz grains in the ground 
contain fluid inclusions, some with spontaneously moving bubbles. 
The larger felspars are chiefly orthoclase, but some plagioclase is 
present; patches of dark-brown iron oxide and secondary epidote 
crystals are results of decomposition. 
Though unable to offer any proof of the age of irruption of these 
igneous masses, or of the relation of the ash, etc., to the Cambrian 
beds of the district, I scarcely think that Dr. Hicks’s view of their 
Pre-Cambrian age is probable; their similar position to that of the 
rocks mentioned above as intrusive among Cambrian shales renders 
it at least desirable that some evidence should be brought forward 
to show why the results of the Geological Survey are not to be 
received; till this is done one had best adopt the most natural 
solution of the structure of the country, viz. that offered by Sir A. C. 
Ramsay in the Survey Memoir on N. Wales. 
To the north-east of Madryn are some peculiar sedimentary beds, 
viz. those seen in the road-cutting where Y Gledrydd stands on the 
