456 E. B. Tawney—Woodwardian Laboratory Notes. 
some of which are partly-decomposed ilmenite. There is a little 
calcite and a few microlithic needles of what may be apatite: the 
slide also contains afew grains apparently of quartz and of secondary 
origin. 
[P. 65.] Variety of trap one mile N.W. of Pwllheli, near Deneio 
on map. A dark green rock of coarse grain, with brown-black augite 
and white or green felspars: no appreciable effervescence with acid. 
Microscope.— A coarsely crystalline rock. Plagioclase felspar 
occurs in long oblong crystals very much decomposed and presenting 
a “saussuritic” aspect: intercrystallized with it is a good deal of 
augite rather more decomposed than in P. 58. Two or three 
secondary products of chloritic nature are present here: one, the 
more serpentinous variety of viridite: another, possibly chlorite or 
a doubly refracting mineral of a serpentinous nature. There are 
irregular grains of iron peroxide, nearly all of which seem to be 
decomposed ilmenite, scattered throughout the slide. There are also 
five or six polygonal grains of a zeolite, apparently not orthorhombic, 
possibly heulandite. The rock may be called a diabase, but has 
evidently been a dolerite. 
[P. 126.] Near Pwllheli, “near the junction of the N. road with 
the turnpike ;” the turnpike indicated is probably about a mile on 
the Carnarvon road. The rock is brownish-grey, of medium grain, 
with blacker spots: very slight effervescence with acid. 
Microscope.—The ground consists of intercrystallized plagioclase 
and augite, and a third olive-green mineral in very variable-sized 
grains. Most of the plagioclase is fairly well preserved, except that 
it shows some decomposition along its principal cleavage planes and 
appears to be traversed by strings of viridite. The augite is in a 
good state of preservation, and shows in many cases transverse 
sections of the prism with the characteristic cleavages. The third 
chloritic mineral occurs similarly to the augite and has the same 
appearance as in [P. 65]. In one part of the slide there are several 
grains of a zeolite rather resembling those in [P. 65], and it is 
noticeable that in the vicinity of these the plagioclase has undergone 
a ‘‘saussuritic”’ decomposition. There are irregular grains of iron 
peroxide seattered throughout the slide, and a few specks of pyrites. 
The rock has evidently been a basalt, but would now be called a 
diabase. 
[P. 88.] Diabase, Porth Vogo, “close to junction.” The locality 
cannot be identified on the Ordnance Map, but from perusal of 
Sedgwick’s Journal, it is apparently from near Llanfaelrhys, the 
junction being with the shales of that district. It is a grey rock of 
fine grain, and contains numerous spots of calcite about 4 inch 
diameter, showing the cleavage planes: even the light grey ground 
effervesces most actively with acid. 
Microscope.—The ground in the slide consists of small plagioclase 
crystals and a translucent green mineral: throughout this is 
scattered a very large amount of iron peroxide, a great deal of 
which is ilmenite. The plagioclase is well preserved and shows its 
characteristic twinning. The green mineral is feebly dichroic and 
