172 



CARBONIFEROUS. 



thickness of 330 feet. At Mynydd Garreg the lower portions con- 

 sist of sandstone and conglomerate, the upper of arenaceous shales 

 and flaggy sandstone ; these indeed are its prevalent characters, 

 the conglomerate being composed of quartz pebbles, the sandstone 

 sometimes passing into quartzite. Large blocks of these rocks are 

 generally scattered about on the line of outcrop. The shales and 

 occasional coal-seams render the boundary-line with the Coal- 

 measures above very vague. The Millstone Grit forms a thin and 

 inconspicuous band north of Cardiff'; but farther west, at Cefn 

 Hirgoed and Cefn Crubwr, the beds stand out in bold ridges, and 

 here the broad outcrop is probably duplicated by a fault. 



As before mentioned, the Millstone Grit is not definitely identified 

 in the Gower peninsula, and it remains to be proved whether the 

 Gower shales should be correlated with it, or whether it be re- 

 presented by certain sandstones above them and now included 

 with the Coal-measures.^ (See p. 167.) At Cwm Afon, near Aber- 

 afon, a seam of coal two feet in thickness, called the Crow's-foot 

 vein, is worked in the IVIillstone Grit. 



On the Pembrokeshire coast the Millstone Grit is represented by 

 hard white sandstone and grit. 



At Bristol the Millstone Grit rises up in Brandon and Clifton 

 Hills. Its thickness in this neighbourhood has been estimated at 

 about 1000 feet. (See Fig. 26.)'* 



Fig. 26. -Section from Durdham Down to the City of Bristol. 

 (R. Etheridge.) 



N.W. 



Reptilian 

 Bed. 



New Red 



Sandstone 



and 



Conglomerate. 



Lias. 



Red Marl 



and 



Dolomitic 



Conglomerate. 



S.E. 



Bristol. 



X^^nKXSVH 



Carboniferous Limestone. 



w 



Coal-measures. 



In the INIendip country sections are rarely seen ; the beds are 

 generally represented by close-grained quartzite with iron-stained 

 spots. The beds have been exposed at Leigh Down, nearWinford, 

 between Mells and Ashwick, and at Vobster. To the south of the 

 IMendips, traces of the rock occur between Easton and Priddy, and 

 near Binder east of Wells. 



In Devonshire the Millstone Grit has not been distinguished, 

 although no doubt represented in the lower part of the Culm- 

 measures, — perhaps by the Coddon Hill Grits. (See sequel.) 



1 Science Gossip, Aug. 18S0 ; see also E. Hull, Q. J. xxxiii. 632 ; De la Beche, 

 Mem. Geol. Surv. i. 143. 



2 R. Etheridge, Q.J. x.xvi. iSS. 



