IRONSTONE FORMATION OF THE FOREST OF DEAN. 
223 
sea level. The watershed is chieflj' on the south-west to the Wye, aud 
on the south-east to the Severn. 
The view from Yorklcy Hill, on a fine day, is possibly one of the 
finest of its kind in England. Looking northward, in the immediate 
foreground, are the steep euttings in Old Red Sandstone of the lower 
road to Blakeney ; and beyond, looking over the Severn, is the wide 
extended plain of Lias, traversed by the sinuous course of the river, 
which teaches, in more than one lesson, how the position of a river- 
channel is determined by the chance hardness or softness of a 
particular bed of rock — by the barriers of sand formed by reflected 
currents, or by a line of faults, thus disclosing, by a panoramic views 
facts that cannot be learnt or comprehended by mere local inspection. 
Considered in its geology, per se, we may describe the Forest basin as 
limited to the old red sandstone for its base, and as having its side 
composed of carboniferous limestone, millstone grit, and coal measures. 
I. Old Eed Sandstone. 
The Old Red Sandstone would entirely surround the basin, were it not 
that its continuity at the surface is broken on the south, where it dips 
beneath the limestone at St. Briavals, reappearing about two miles to 
the east at Bream. 
The beds which immediately underlie the limestone-formation have 
an average thickness of about fifty yards, and are equivalent to the 
uppermost beds of the Devonian rocks ; but, from their graduation into 
the limestone-series, there is probably good reason for their classification 
with the lowermost members of the Carboniferous group. 
In the aggregate they number some thirty-five beds, which may be 
observed in bold section on the road from Mitcheldean to Ross, near 
the Lower Lea Baily enclosure, and whore they are seen to consist of 
grey and red sandstone, with occasional thin bands of marl ; the 
cliaracter of the sandstones being sometimes micaceous. The 
marls are usually claret-coloured, red, and green, but the presence of 
per-oxide of iron in the sandstones is rather the exception than other- 
wise. The resemblance between many of the upper old red sandstone? 
and those of the true coal-measures is not a little striking, and, some 
years since, led to a fruitless sinking about a mile north-west from the 
ruins of Penhow Castle, but which might have been prevented had 
observations been extended further to the south-east, where the car- 
