1822.] Geology of’ Snowdon, and the surrounding Country. 333 
the south-east at about 68°. On the sides of the quarry were 
perceived numerous fissures possessing a certain degree of 
parallelism among each other, though wanting completely that 
evenness and continuity which belong, generally speaking, to 
the lines of regular stratification; and as these fissures are 
nearly horizontal, they serve materially to assist the quarry-man 
in his operations: fissures in a downward or almost vertical 
direction nearly at right angles to the cleavage plane, are less 
common, but experience has proved that the slates in mass may 
be split with considerable ease in this direction, though without 
producing an even surface ; thus reducing them into fragments 
partaking more or less of the rhombic form common to slates 
after long exposure to the action of the atmosphere. 
As the slates of this quarry dip uniformly towards or under 
the northern termination of the mountain at the foot of which it 
is situated, we became desirous to ascertain the nature of the 
rocks constituting the high ridges crossing in the direction of 
north-east and south-west, the higher parts of the acclivity, and 
which of course are incumbent on the slates. Ascending, there- 
fore, we cautiously examined every rock in situ to a considerable 
height. For some distance we found only a purplish slate ; but 
the following sketch will serve to explain what we perceived : 
fan 
i " 
f}) 
Wy PH 
1 ae y 
Mf] Qaeerry 
a. Continuation of the quarry slates, but less firm, and of a 
purplish colour. 
6. A granular rock, yet somewhat slaty, resembling the base 
rock of Moel Shabod, and effervescing by the application of 
acid, 
c. Green slates, resembling chlorite slate. 
d. A green granular rock, containing round masses of calcare- 
ous spar, decomposing on the surface. 
e. Slates. 
f- A rock chiefly resembling d, but containing abundance of 
crystallized quartz, and occasionally chlorite: effervesces in 
patches; but in some places appears to consist chiefly of 
steatite. 
g. Very hard slates of a greenish colour. 
h. Rocks resembling fand d. 
Most of the rocks and slates of the preceding sketch greatly 
Ff 
i) : 
Li 
