of the Forest of Dean Coal-field. 197 



stow Park to Wentwood on the Usk ; and that it is overlaid by the new red 

 sandstone near Newport on the same river. 



This conglomerate or hard grit, it may be scarcely necessary to observe, is 

 some way below the top of the old red; and it sometimes forms two distinct 

 beds*. 



The hardness, as well as the number of the pebbles, varies ; but there is 

 scarcely a place along the outcrop of the old red, where fragments at least, of 

 the conglomerate, are not seen (except north-east of Lydney, where the con- 

 glomerate is cut off by the fault) ; and it usually presents a steep ridge, suc- 

 ceeded by the soft ground of the upper beds and of the limestone clay. These 

 argillaceous strata often throw out springs, accumulated in the limestone rocks 

 above f. 



The upper bed of the old red sandstone, is given in Mr. Mushet's sec- 

 tion as twenty fathoms in thickness ; and it rests immediately on the conglo- 

 merate. 



The Penyard and Chase Hills, near Ross, (Map, PI. XV.), are outliers of 

 this upper bed and the subjacent conglomerate, the latter constituting, all 

 around the hills, projecting masses which dip about 12°, so as to take the ground 

 again, and form the rugged and picturesque scenery from Hope Mansel, and 

 the bold promontory of the forest coal-field south of Lea, as well as the escarp- 

 ment by Warm Hill, Goodrich, and Huntsham to the Doward and "Buck- 

 stone," where a highly inclined mass of it, forms an object of interest to the 

 antiquary as well as to the geologist. 



The similarity between the conglomerate bed of the old red sandstone and the millstone grit, 

 has led some miners to sink for coal in the former, about a mile to the north-west of Penhow. 

 Had they extended their observations, on the surface, a little more to the south-east, they would 

 have seen the carboniferous limestone, which must have been familiar to them, dipping conformably 

 to, and resting upon, the strata they were piercing ; and they would have saved much expense and 

 waste of time. 



At Bircham Hill, near Newland (3^ miles south-east of Monmouth), the 

 old red sandstone appears to have been forced up through the carboniferous 

 limestone ; a supposition which is strengthened by the strata dipping in every 

 direction ; but it must be observed, that the valley from Newland to Red- 



* At Chapel Hill, near Lydney, there seems to be a second upper layer of it very distant from 

 the first, but this appearance may be due to a fault. Near Monmouth, at the Kimin Hill, and 

 Buckstone, there are similar indications, and the conformation of the ground, and a general view 

 of the hills from Trelleck to Penhow, would lead to a similar conclusion. 



t A very micaceous stone sometimes occurs in the upper part, near the conglomerate. Quartz 

 pebbles are sparingly dispersed in beds above the hard congtonjerate, and for some way below it. 



