ANNALS 
OF 
PHILOSOPHY. 
NOVEMBER, 1822, 
ARTICLE I. 
Sketch of the Geology of Snowdon, and the surrounding Country. 
By W. Phillips, FLS. MGS. and 8. Woods, MGS. P 
Tne structure of North Wales, as far as our knowledge 
extends, has hitherto but ina slight degree excited the curiosity, 
or exercised the judgment of any person conversant with geolo- 
gical inquiries. It has been assumed, however, that in North 
Wales the vallies are occupied by clay-slate, and the mountains 
or their summits by greenstone. ‘The discovery of organic 
impressions near the summit of Snowdon created doubts which 
were not easily solved ; and while some affected to dispute the 
accuracy of the observers, others accounted for it by gratuitous 
suppositions. We believe that no part of this country can be 
called primitive, and that neither greenstone, clay-slate, nor grey- 
wacké, is any where to ve found in the district of Snowdonia : 
in this term we comprehend the mountain range bounded on the 
east by the Vale of Conwy, extending a line southward to Festi- 
niog: on the north by the Bay of Beaumaris: on the west by 
the Menai Strait carrying on a line from Carnarvon to Pwhhellie, 
and on the south, from thence along the coast of Cardigan Bay, 
through the Vale of Festiniog. 
In our opinion this district offers a new and highly interesting 
field of investigation to the geologist. The partial examination 
of its various rocks, and especially of their extremes, would 
inevitably lead to the conclusion that they are of different form- 
ations, and possess distinct characters : a more extensive survey 
affords satisfactory evidence that most, if not all, of them, gra- 
New Series, vou. Iv. Y 
