Dr. T. F. Sihh/—The Forest of Dean Coalfield . 421 



Ruspidge, the base of the Coal Measures passes rapidly eastward 

 across the remainder of the Carboniferous Limestone Series, on to the 

 Old Eed Sandstone. The Carboniferous Limestone remains concealed 

 by Coal Measures for a distance of some 3 miles south of How- 

 beach Colliery ; it reappears near Lydney, at the southern end of 

 the coalfield. 



Close to Howbeach Colliery, in the gorge of Blackpool Brook, an 

 old quarry shows the unconformable junction of Coal Measures and 

 Carboniferous Limestone. The quarry-face shows dolomites belonging 

 to the Main Limestone, dipping north-westward at about 60°, over- 

 lain by Coal Measure sandstones which dip westward at a small angle. 



On the northern margin of the coalfield, west and north-west of 

 Drybrook, the beds of the Carboniferous Limestone Series, being 

 gently inclined, cover a large area. Not far west of Drybrook, the 

 Drybrook Sandstone is overstepped by the Coal Measures. Farther 

 west, beyond Kuardean, the Coal Measures rest upon the Main 

 Limestone ; while to the north of Ruardean, across the valley, a large 

 outlier of Coal Measures reposes directly upon the Lower Limestone 

 Shales at Howie Hill. 



Some of the features just described have been noticed by earlier 

 writers. In particular, the interruption of the Limestone-outcrop 

 on the south-eastern border of the coalfield, between Howbeach 

 Colliery and Lydney, was noticed by Buckland and Conybeare,' who 

 attributed it to a fault ; and the same phenomenon was discussed 

 and very clearly illustrated by Maclauehlan.^ 



H. D. Hoskold, writing in 1892, stated that near Howbeach 

 Colliery "the Pennant rocks belonging to the Lower Coal Measures 

 rest immediately upon and are in contact with the Carboniferous 

 Limestone ".' 



Quite recently Mr. Newell Arber, in his important paper * on the 

 fossil flora of the coalfield, has discussed the relation of the Coal 

 Measures to the underlying strata at some length. He writes as 

 follows: — 



"Reviewing the present evidence I am inclined to think that it 

 will eventually prove that an unconformity exists a short distance 

 below the Lower Trenchard Coal perhaps a little above the Sandstone 

 vein of Iron Ore. In this case the greater portion of the Millstone 

 Grits, so-called, will be found to be simply a sandy facies of the 

 Carboniferous Limestone Series, just as the lower beds have already 

 been shown to be by Dr. Vaughan. I imagine that, in the Forest of 

 Dean, the Upper Coal Measures rest unconformably on an ancient 

 floor consisting for the most part of the higher sandy beds of the 

 Carboniferous Limestone Series, though, in some parts of the area, 

 on Carboniferous Limestone of normal facies or even on Old Eed 

 Sandstone . . . Owing to the general absence of sections, the 

 unconformity has not, however, been demonstrated in the field. 

 True Millstone Grits, Lower, Middle, and Transition Coal Measures 



^ Trans. Geol. See, ser. n, vol. i, p. 286, 1824. 

 2 Trans. Geol. Soc, ser. II, vol. v, pp. 204-6, 1837. 

 ^ Proc. Cotteswold Nat. F.C., vol. x, p. 135, 1892. 

 * See n. 5, p. 420. 



