212 
ON THE GEOLOGY OF 
of the Conway is situate to the north of the range, it will 
be necessary that we may acquaint ourselves more particu- 
larly with its general characters, and contents, to descend 
the mountain, and traverse in all directions the valley. 
Accordingly, on examining it, we shall find that, in 
length, from north to south, it extends upwards of twenty 
miles, in breadth scarcely eight ; at the southern end, for 
seven or eight miles, it is very narrow and confined, and, 
towards the centre, it gradually enlarges itself to its great- 
est dimensions, and maintains nearly the same breadth to 
the mouth of the Conway. 
On the west, or Carnarvonshire side, it is separated from 
the Menai basin by the Snowdon range ; on the east side, 
it includes a part of Denbigh, cut ofi" from the remainder 
of that county by a low ridge of hills, running parallel with 
the more lofty hills of the western side of the basin. 
The prevailing rock of this valley is transition-slate; 
and it is observed, that, where it is hardest and least de- 
composable, the features of the basin are more rugged and 
bold ; and the reverse, when this slaty rock is less tenacious. 
Agreeable to this idea, it is found that the higher portions 
of the Conway basin, surrounded by such unyielding rocks, 
is wild, broken, and irregular. And as we descend north- 
wards along the course of the Conway, softer and more 
pleasing appearances present themselves to the eye. 
The mountains on the west, or Carnarvon side, are lofty 
and abrupt, and, from their vertical structure and unyield- 
ing composition, off'er a peaked, varied outline. And from 
the long resistance these slaty mountains make to the ac- 
tion of water, a series of small lakes are met with at their 
base, being the fountains of as many streams which burst 
through the covering of wood, and find their way into the 
interior of the basin. 
Among the principal rivers of this district are, the 
