222 ON THE GEOLOGY AND STATISTICS 
means of creating wealth and industry in a country. Such 
a one will find this district abounding in minerals and me- 
tals of a highly important kind. 
We have already observed, in describing, generally, the 
mountain chain of Snowdon, that the rocks of which it is 
composed have for the most part a slaty vertical structure ; 
and, except on the eastern and southern faces of Snowdon 
itself, and in a few other places of this range, where some- 
what of a columnar basaltic formation appears, the slaty 
vertical structure, more or less, may be said to characterize 
the whole chain of Snowdon. 
Though such great masses of slaty rocks everywhere 
abound, they are not always of a quality fit for use. The 
best is found in a line north and south, between the south 
bank of the Ogwen, where it issues from the wild and 
rocky glen of Nant Francon, and the eastern bank of the 
lakes of Llanberris ; and in another line, in the same di- 
rection, but at some distance from the first, stretching 
from the western bank of the lower lake of Llanberris, 
viz. at Glyn to Nantle and Llanlyfne lakes. Between 
these two lines are several parallel slate veins wrought at 
present. But in many other places in the Snowdon range, 
as perceived in sections exposed to view by the streams 
running through the deep dingles they have formed, other 
similar parallel veins of slate crossing them are traceable. 
These veins are found frequently to alternate with very 
hard rocks, approaching in appearance to the hardest ba- 
salt and greywacke ; at other times, again, with very hard 
darkish black and light coloured quartzy rock, which as- 
sumes the same vertical structure as slate; — and the best 
workable slate is always found to be that which is enclosed 
in such a hard rock. 
