E. B. Tawney—Woodwardian Laboratory Notes. 457 
doubly refracting with a slightly fibrous structure; it occurs in scales 
and larger masses, in which latter case it is associated with epidote 
and probably replaces augite. There are several large amygdaloids 
of calcite in this slide, one of which contains near its edge five or six 
well-defined hexagonal quartz crystals. 
The rock is now a diabase, and was once probably a vesicular 
basalt. 
[P. 12.] Third trap dyke between Nevin and Porth Dinlleyn—The 
hand-specimen shows a good deal of pyrites ; it isa dark green rock 
of medium grain, the constituents not marked out by any great 
difference of colour: abundant effervescence with acid. 
Microscope.—Consists of very much decomposed plagioclase and 
augite. The plagioclase has undergone a “saussuritic’”’ decom- 
position, and the augite is traversed by cracks which are lined with 
decomposition products. Anastomosing veins of isotropic viridite 
permeate the whole slide. There is some calcite present, and a great 
many grains of iron peroxide, the chief part of which is ilmenite, 
are scattered throughout the slide. The rock is a diabase.—A.S. Rerp. 
[Cl. 15.] Hornblendic diabase, “tumbled” block under Gyrn Goch, 
near Clynnog; a greenish to brownish-black rock, coarsely crystal- 
line, with bright cleavage planes of bronze-coloured bisilicates ; there 
is an absence of any white material: no effervescence with acid 
noticeable. Copper pyrites grains are seen in it. 
Microscope.—This rock is crystalline in structure, consisting of 
more than one form of hornblende, augite, decomposition products 
replacing felspar, and grains of black iron peroxide. These 
secondary microlithic products have so obliterated the structure of 
the felspar that it is difficult to come to any conclusion about the 
species; one or two crystals, however, seem to retain faint indica- 
tions of plagioclase twinning. Of the hornblende, some is the dark- 
brown strongly dichroie variety, some a pale-green kind, and perhaps 
a little of an acicular type, a sort of actinolite. The green horn- 
blende is probably a secondary formation after augite, and so may 
be called uralite. Some of it is also very closely ‘associated with 
the brown variety, as though formed from it, or as if both were 
alteration products. There is also a secondary product of a serpen- 
tinous nature. A fair amount of unaltered augite is still present. 
The magnetite (?) grains are not usually associated with the horn- 
blende or augite. There is also very probably some siderite. It is 
difficult to affix a name to the rock, perhaps hornblendic or uralitic 
diabase would be the best. 
[Cl. 17.] Hornblende diabase, loose block under Gyrn Goch; a 
coarsely crystalline rock speckled brown and white, with lustrous 
cleavage planes of the bisilicates; there is considerable effervescence 
with acid. 
Microscope—A general similarity to the last, except that the 
hornblende is rather more platy or bladed, possibly also a little 
delessite or some kindred mineral. One or two grains of a yellowish 
mineral of rather granular structure (? sphene). 
[Cl. 24.] Hornblende diabase, below the turnpike in situ, not far 
