408 . ° Messrs. W. Phillips‘and S. Woods on the > [Dec. 
sand, among which may be found very small fragments of a 
white crystalline substance. At the base of the cliff it is of 
considerable width, and appears to divide into branches, but 
we did not perceive any alteration in the limestone traversed by 
it, in regard either to direction or texture; but above, where 
immediately in contact with the dyke, it appeared to be a little 
turned upward, an appearance which might be the consequence 
either of the unevenness of the surfaces, or of our not standing 
so as to bring the eye on the same plane as the stratification of 
the layers of the rock, the ground being very unfavourable. 
As we travelled from Bangor to Carnarvon in the evening, we 
had no sufficient opportunity of observing the nature of the 
country between the two places. 
As the weather had now become more favourable to the 
ascent of Snowdon, we determined to attempt it from the side of 
Llyn Cwellyn by the copper mine road, about seven miles south 
of Carnarvon. 
The first five miles of the road from Carnarvon scarcely 
afforded the appearance of a rock zm situ, but only a few boul- 
ders, the country on either side of the road being well covered 
by herbage, until we arrived at the foot of Moel Eilio on the left, 
which presented nothing near the road but, slates greatly resem- 
bling some on Moel Shabod, and above Nant-francon quarries, 
and apparently partaking more of the nature of steatite than of com- 
mon slate: they split into thin Jamine, are hard enough to seratch 
glass, and are green by transmitted light: they have the usual 
direction of NE and SW. On the right, the foot of Menydd 
Mawr presented a somewhat singular porphyritic rock. It 
appears to consist of transparent crystals of quartz and of felspar, 
included in a paste which, although it is hard, and yields with 
some difficulty to the knife, we believe, from its weathering, to 
be a species of steatite ; but it has at first sight greatly the 
resemblance of compact felspar. This rock resembles one of 
the varieties of the summit of Moel Shabod, except that it wants 
the crystals of augite, manifestly imbedded in the latter. 
Immediately after quitting the house of the guide on the bank 
of Llyn Cwellyn, we passed somelarge boulders fallen in all pro- 
bability from Monydd Thevedo ; they bore a considerable resem- 
blance to the rocks of the summit of Moel Shabod, but we did 
not afterwards find any masses of the same variety im situ either 
in the ascent of Snowdon, or upon the mountain itself. 
About the first two miles of ascent are along a horse road 
made by some Cornish gentlemen engaged in working a copper 
mine not very far beneath the summit of the mountain on the 
opposite side : by the displacement of the grass and thin cover- 
ing of alluvium in forming this road, we could perceive that no 
other rock prevails along it, quite to the eastern ridge above 
Cwm Clogwin ; nor did we perceive any other rock 2m sifu ris- 
