4 
PENMAENMAWR. 
* 
After a blast, tlie men loosen the shaken masses with crow¬ 
bars, their safety being as far as possible secured by ropes 
fixed at the top of the face of the rock on which they are 
working. 
An examination of the rock in this section shows that it is 
composed of felspar, and a rhombic pyroxene, with a very few 
crystals of augite. The felspar is in the usual elongated 
forms and is triclinic, but its exact species is not certain ; 
although from the fact that six extinctions were measured 
betwen 54° and 56°, it is almost certain that labradorite 
is present. In specimens from this quarry it is pretty fresh 
and free from decomposition, but in other parts it is not in 
such good condition. The augite and the enstatite are very 
similar in appearance, and where the plane of the section 
has happened to cut across the prism I do not think they are 
distinguishable. They are both pale in colour—the augite is 
perhaps a little darker. When the section is more or less 
parallel to the prism, however, the difference of crystal 
system is at once shown. Speaking generally, the long 
narrow sections of enstatite “ extinguish ” when the length 
is parallel to the principal plane of one of the nicols prisms, 
whilst in the case of the monoclinic augite this only happens 
in the case of the section being in the zone of the ortho- 
pinacoid and base. In all other cases, and they are natu¬ 
rally likely to be much the most numerous, the length of the 
crystal when it “extinguishes” makes an angle with the 
planes of the nicols, which may vary from 40° downwards. 
The colours in polarised light which the enstatite shows are 
paler and more washed out than those of the augite, and the 
latter does not show the slight dichroism which charac¬ 
terises the former, giving a green or yellow tint according to 
the position of the crystal section with regard to the principal 
plane of the polarising prism. Some of the crystals are 
twinned. When some decomposition has taken place the 
pyroxenes are replaced by a fibrous green mineral. 
Of this constituent of the rock Phillips says :—“ The 
form of these crystals is seldom sufficiently perfect for com¬ 
plete identification, but some of them are strongly dicliroic, 
and their structure is that of hornblende ; others, which are 
very pale in colour, are not distinctly dicliroic.” The colour 
he describes as “ light greenish brown.” 
A few flakes of light brown mica are met with here and 
there, characterised by their strong dichroism and pronounced 
cleavage. 
Irregularly distributed through the stone are certain grey 
veins and patches of apparently coarser texture, cnlled by the 
