PENMAENMAWR. 
So far as I know, tlie character of the rock has been 
mentioned only by Professor Rosenbuscli, Mr. J. A. Phillips, 
and Mr. J. J. Harris Teall. By the former it is stated that 
“ the traps of Penmaenmawr and Conway, in North Wales, 
belong to the Enstatite-bearing Diabases, of which they are 
indeed most typical examples.” Mr. Phillips, in a paper in the 
“Quarterly Journal of the Geological Society,” 1877, p. 428, 
gives a detailed account of the varieties to be observed in the 
mass, giving analyses showing the different stages of alteration, 
and a description of the mineralogical character as deter¬ 
mined microscopically. He considers the mineral associated 
with the felspar to he hornblende, recognising its slight 
dichroism but overlooking its rhombic crystallisation. I 
shall have to refer to this paper again later on. Mr. Teall 
tells me that he has mentioned the Penmaenmawr stone in 
his paper on the Whin Sill of the North of England, which 
he read before the Geological Society in June, but the paper 
has not yet been published, so I cannot say to what extent 
he has investigated it. I believe, however, only so far as to 
confirm the description given by Rosenbuscli. The specimens 
which I obtained while staying at Llanfairfechan this sum¬ 
mer are all from the western end of the mass, which, how¬ 
ever, Phillips states to be the least altered by weathering. 
On making our way towards the quarry we find, as soon 
as we get clear of the village and come upon any rock, that it 
is slate, the planes of cleavage (or deposition) dipping towards 
the igneous mass, though probably the dip is not much 
affected by the latter. This continues until we arrive at the 
rough wooden ladders which the quarrymen have fixed in a 
cleft in the rock to facilitate their laborious journey to and 
from work. Here we find the igneous rock, and can trace it 
inwards, gradually changing in character for a few feet. The 
first we come to is split up into quite thin plates, and this 
structure, on a large scale, gives its peculiar appearance to 
the line of cliff which forms the boundary of the mass. 
A little further in the rock is very compact, sometimes 
of a light grey colour, sometimes almost black, but usually 
containing a quantity of white patches which are either 
felspar crystals or minerals replacing them. On examining 
a specimen of this microscopically, we find it to be almost 
entirely made up of interlacing felspar crystals, with 
occasional porpliyritic ones of larger size, and in the inter¬ 
stices I think we may detect a small amount of residual 
glassy matter. In one specimen, which, however, I got from 
a wall in the village, there are dark veins and patches which, 
on examination, proved to be the parts where the felspar is 
