332 Messrs. W. Phillips and S. Woods on the [Nov. 
the knife, though here and there yielding to the action of acid ; 
also other varieties more decidedly slaty, of a yellowish or green- 
ish colour, and softer. The following varieties of rock were also 
found in the pass. Masses resembling in every respect the 
base rock of Moel Shabod, inclosing others of a darker colour, 
which also were softer, and very decidedly steatitic. Very large 
masses of the same rock, often highly steatitic, enclosing flinty 
slate, in pieces from the size of a pea to that of the human heaa. 
A steatitic rock composed of small particles of various colours, 
forming in the aggregate a paste of a greenish hue, enclosing 
(apparently) angular picces of flinty slate. Red and white horn- 
stone enclosing translucent quartz and steatite. It could be 
perceived only on the weathered surfaces of many of these 
rocks that their structure was slaty. 
Our curiosity was naturally directed to ascertain whether the 
large slate quarries of Nant-francon constitute a part of the 
eneral series or not. These quarries are situated near the foot 
of the northern termination of a mountain, a little on the west of 
the road from Capel Curig to Bangor, about two miles beyond 
the Inn at Tyn y Maes. They consist of three principal cavities, 
averaging, perhaps, 200 to 300 feet in depth, by as many in 
length and width. About 950 men and boys are employed in 
quarrying, splitting, and trimming the slates. The best are not 
blasted, but split by wedges parallel to their cleavage plane; and 
thus thick masses are obtained, which again are split by means 
of a mallet, and the application of the edge of a broad and sharp 
chisel parallel to the Jamine. The slates are of two principal 
colours; viz. of the ordinary slate colour, and of a purplish or 
réddish hue: the latter are considered as the best slates, being 
of a finer grain, and splitting readily into thinner lamine than 
the others : occasionally there appear specks or large patches of 
a green colour, also having a slaty fracture, but of a closer grain, 
very much harder, and translucent on the edges. The quality 
of the slate often varies greatly ina few yards, or even feet. 
In what degree the slates of this quarry partake of the nature 
of chlorite, it is, perhaps, impossible to determine; it is very 
certain, however, that the irregular surfaces produced by fractur- 
ing the slate in a direction opposite to its cleavage present a 
granular aspect and glimmering lustre much resembling chlorite, 
and that a considerable but very irregular vein of quartz and 
chlorite accompanied by calcareous spar, traverses the slates, 
the chlorite being sometimes in a crystallized state, sometimes 
in the form of slaty chlorite; large masses of the latter are 
observable on the south-eastern part of the quarry, and those 
blocks of it were very numerous, as were also rolled masses of 
it ‘in several parts of the works. 
The cleavage plane of the slates here, as every where else, is 
in the direction of north-east and south-west, and dips to 
