THE GEOLOGIST. 
MAY, 1858. 
THE PHYSICAL STRTiCTUEE OF MERIONETHSHIEE AND 
CAERNARVONSHIRE. 
By Professor A. C. Ramsay, F.R.S. and G.S. 
ThE view from the summit of Cader Idris is one of the most 
magnificent in Wales. Turning to the south, the landscape con- 
sists of a series of rolling hills, stretching as far as the eye can 
reach, in smoothly swelling outlines; and it is impossible not to 
be struck with the circumstance that, though some rise higher than 
others, they maintain a sort of average height, accompanied by a 
general gentle inclination towards the sea. Through this broad 
undulation innumerable valleys have been excavated. The hills have 
not been formed merely in conseqTience of disturbance of the strata ; 
but, through the outcropping and smoothed edges of disturbed strata, 
many great and small valleys have been cut by old marine denudations, 
atmospheric disintegrations, and the action of running water. The 
general uniform character of the outlines of this country is due to the 
sameness of the rocks, which, in the main, consist of slates, occa- 
sionally varied by hard or interstratifiod bands of sandstone, the whole 
belonging to that part of the Silurian series known as the Caradoc or 
Bala beds, and the rocks immediately overlying. 
Turning northwards, a change in the character of the landscape 
becomes at once apparent. The mountains are broken and rugged. 
The summits of the Arans, the great swelling mass of Rhobell-fawr, 
the cliffs of Rhi nog-fa wr and Rhinog-fach, that guard the pass of 
a 
