400 PKOF. J. r. BLAKE ON THE MONIAN AND 



innumerable grains of uniform size following more or less the appa- 

 rent stratification, but it contains too some larger crystal fragments 

 of felspar and zircon. A third, which is very dark, has the uniform 

 grains still better stratified in the midst of diffused dust. The grains 

 appear to be of felspar rather than quartz. This group does not, 

 as I expected it w^ould, leave absolute conviction on the mind that 

 it is derived from the neighbouring underlying series ; but this 

 much may be safely said, that no such rocks have been found as yet 

 forming part of the volcanic series of the neighbourhood, and they 

 are very like the neighbouring slates and grits. Certainly the 

 evidence of these contained pebbles is favourable rather than other- 

 wise to the unconformity observed in the field. 



To return to the stratigraj^hy proper. After passing the con- 

 glomerate in a journey towards the west, we come again to a vast 

 mass of purplish grit, which, as before, shows little sign of stratifi- 

 cation, but is much intruded upon by masses of greenstone. Where- 

 ever any bedding is seen, as east of Church Pulverbatch, the strike is 

 still to the jST.N.E., and the dip nearly vertical. After passing a 

 varying breadth of this grit, we come upon the mass of rock which 

 forms the middle portion of the series. This, though mentioned by 

 Murchison as " alternations of strata identical with those described," 

 seems generally to have been overlooked. If we make a traverse in 

 various latitudes, we find towards the south more than two miles' 

 breadth of solid purple slates, always dipping at a high angle 

 towards the west, and with an average N.N.E. strike. The whole 

 hill on which Wentnor stands is composed of this rock, and it 

 may be traced in numerous exposures as far as Norbury. The 

 breadth is little less in the traverse through Medlicott farm and 

 Gravenor, though many thin bands of grit are hereabouts inter- 

 calated. jN'ear Eatlinghope the breadth is reduced to about a mile, 

 but the rock is admirably seen in the highroad at Bridges, and a 

 little further N. on the hill above Stitt Parm, though everywhere 

 within its range it may be easily traced. In the neighbourhood of 

 Cothercott it is reduced again to about a quarter of a mile, which it 

 never again exceeds. No exposures of the slate are seen north of 

 Castle Pulverbatch, but the last relic of it may be recognized in the 

 quarry north of Longdcn Common. This slate may be easily dis- 

 tinguished from those of the older series (except in the neighbourhood 

 of Mindtown) hj its greater massiveness, and by the absence of the 

 numerous subdividing, cleavage-like planes. Its occurrence in the 

 middle between two masses of grit may seem to indicate a synclinal, 

 but the dips observed give no countenance to this idea ; there is not a 

 single reversed dip in the whole area. We may perhaps think of an 

 isoclinal, but in such a case we should expect the boundary to be 

 more regular than it is ; the eastern boundary, in particular, is by 

 no means a straight line. In tracing these boundaries, however, a 

 new feature occurs which is very instructive when contrasted with 

 the inferior limit of the grit, where, as has been seen, it is also in 

 contact with slate. On both sides of this upper mass of slate there 

 is abundant evidence of its intercalation with the grit, so that the 



