1822.] Geology of Snowdon, and the surrounding Country. 327 
slates with the rocks of the base invariably takes place parallel 
with the ordinary cleavage of the slates, and wherever this 
appearance is observable, it is always in the same direction; the 
cleavage of the slates ranging, as has already been noted, 
uniformly on this mountain, and in every place we visited (one 
instance only excepted) east of north, and south of west. 
The dip of the slates, however, on this mountain is by no 
means regular: in the upper part of their range on the se te 
side, they are nearly vertical, while on the southern side, they 
dip at a considerably low angle towards the north-west ; but 
in the middle region towards the south-east, at an angle of 54°, 
The slates, as well as the rocks of the lower region, both 
where they are interstratified, and where they appear separately, 
have a remarkable tendency to assume the form of steps, or 
terraces, which is considered to be characteristic of rocks 
belonging to the comprehensive trap formation, as well as in 
another particular, namely, in assuming a semi-globular form, 
which does not seem to he the consequence of atmospherical 
action: this appearance was observable in very numerous 
instances on this mountain, and elsewhere. 
There is one circumstance relating to the stratification of the 
slates and slaty rocks of this mountain which deserves mention, 
because it involves appearances that would tend to mislead, 
without sufficient investigation. It is well known that slates 
have a tendency to separate into arhombic form; and in several 
’ instances on this mountain, the lines at which the slates would 
so separate were remarkably distinct on masses presenting a 
surface of 20 or more feet every way. But these lines of appa- 
rent, and often of actual separation, were much stronger than 
those of the slaty cleavage, being continuous quite across the 
surface of the mass, at about a foot apart, and above an inch in 
width and depth, assuming, therefore, the appearance of lines of 
regutar stratification. The following sketches show the appear- 
ances observed on two neighbouring surfaces, of which the 
lightest lines, representing the slaty cleavage, are in the same 
direction in both; while the lines of apparent stratification are 
in opposite directions, both nevertheless tending to produce the 
rhombic form, 
\ 
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NX. XNX 
The extremely unfavourable state of the weather did not per- 
mit that nice examination of the rocks of this mountain, which 
alone would have enabled us to detect any vestiges of organic 
remains, if any exist inthem. In the garden wall of the Inn, 
