IRONSTONE FORMATION OP THE FOREST OF DEAN. ^23 



sea level. The watershed is chiefly on the south-west to the "Wye, and 

 on the south- east to the Severn. 



The view from Yorkley 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 cuttings in Old Eed Sandstone of the lower 

 road to Blakeney ; and beyond, looking over the Severn, is the wide 

 extended plain of Lias, traversed by the sinuoiis 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, hy a panoramic views 

 facts that cannot be learnt or comprehended by mere local inspection. 



Considered in its geology, ^;^r se, we may describe the Porest 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 Sahdstoxe. 



The Old Eed 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 Eoss, near 

 the Lower Lea Baily enclosure, and where they are seen to consist of 

 grey and red sandstone, with occasional thin bands of marl; the 

 character 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 sandstones 

 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- 



