MAY HILL ANTICLINAL — FLAXLEY, ETC. 



445 



of those transverse faults alluded to. It will be further observed that the mass broken 

 off to the south of this fault acquires a slight change of strike. 



The ending of the May Hill ridge in a single narrow point at Flaxley, is analogous 

 to the terminating point of the anticlinal at Corn-y-fan in Brecknockshire. (See p. 338 

 and wood-cut.) In both cases the narrow form of the uplifted mass, precludes the 

 possibility of its exhibiting a perfectly symmetrical outward dip, one side being brought 

 abruptly against the edges of the overlying strata. There is, however, this difference 

 between the two cases : that of Corn-y-fan indicates the elevation of the uppermost 

 beds of the Silurian System, which on one side, as well as at the point of the anticlinal, 

 pass gradually and conformably into the Old Red Sandstone ; whilst the rock at Flaxley 

 is a sharp wedge, rising unconformably through the surrounding rocks, with which it 

 is not connected by any beds of passage. This little boss of Silurian rock marks the 

 precise boundary line between the Old and New Red Sandstone, the relations of the 

 three formations being explained in the diagram. (PL 36. f. 13.) To the west of the 

 Silurian rock, the Old Red consists of deep red argillaceous marls, in parts spotted 

 green, in short, precisely a poikilite 1 , undistinguishable from many marls of the New 

 Red. It contains small green and red concretions of hard marl, approaching to lime- 

 stone, and some thin flags of micaceous sandstone. Owing to its incoherent nature, the 

 stratification of this disturbed mass of Old Red Sandstone is not clearly marked; 

 but in one part it appears to dip under the Silurian rock, against which it is brought 

 by a longitudinal fault. On the east side, on the contrary, the New Red Sandstone, 

 consisting chiefly of beds of thin, flaglike marl of light green and dingy light red colours, 

 advances to the edge of the boss of Silurian rock, in strata inclined only a few degrees 

 to the east. These discrepancies of position are precisely what we should expect to find ; 

 the undisturbed condition of the new red marl clearly proving, that the anticlinal was 

 formed anterior to the deposit of the keuper or upper strata of the New Red Sandstone. 



The boundary line between the Old and New Red Sandstone passes southward to the east of 

 Newnham, but its exact place is not always easily determinable, owing to the rounded outlines 

 and slopes of the hills. Having, however, the proofs at Flaxley, that the New Red has not been 

 thrown up along this line, all the lower grounds on the eastern side may, it is presumed, be com- 

 posed of that rock, though its surface is often much obscured by a thick spread of fragments of 

 Silurian rocks, Old Red Sandstone, coal grits, &c, derived from the adjacent districts. The two 

 parallel main roads to Coleford and Little Dean enable us, however, to mark the allinement with 

 tolerable precision. That leading to Little Dean has been cut through an arched mass of the Old 

 Red, near the junction with the New Red Sandstone, the beds of which dip sharply to the east and 

 west, and thus mark the continuance of the anticlinal of May Hill and Flaxley. Again, to the south 

 of this spot, the form of the land indicates the continuance of the line of dislocation, and near 

 a farm called Aram, thin-bedded grey Silurian rocks appear 2 . 



1 See note on the term "Poikilite," p. 27. 



2 This was first noticed by Mr. MacLauchlan, of the Ordnance Survey, in the geological map of the Forest 

 of Dean, to which I have already adverted, p. 80. 



3 K 



