108 MR. H. LAPWORTH ON THE [Feb. I9OO, 



boundary-hedge, where it is cut out by a fault running from 

 Llanfadog-Uchaf stream to Pen-y-rhiw Farm. The conglomerate- 

 group is for the most part obscured with Drift, in the proximity 

 of the dislocation. It is inferred, however, that it follows more or 

 less parallel to the Gafallt Beds. 



(3) Pen-y-rhiw. 



The Lower Conglomerate (Ba x ) runs on continuously to 

 Pen-y-rhiw Cottage, where it dips at about 20° north-westward. 

 A section from the cottage to Fron-dorddu Farm (fig. 13, p. 106) 

 practically follows the slope of the beds, and is useful for deter- 

 mining the succession at the eastern end of the hill. A deep hollow, 

 equivalent to a vertical thickness of less than 50 feet, separates 

 the two conglomerates, each of which measures approximately only 

 100 feet in thickness. At most, 50 feet of the Upper Conglo- 

 merate (Ba 9 ) is exposed ; but this, as before, is readily recognized 

 by its proportionately large number of white vein-quartz pebbles. 

 The base of the Gafallt Beds (Bb) is signalized by an abrupt 

 change in the gradient of the ground-surface ; and at the uppermost 

 gate on the path from Coppa Farm to Bwlch Coch Farm a small 

 exposure of the Alonoc/raptus-Sedgivickii Grits (Bb } ) may be 

 seen in the rill at the side of the lane, and in the lane itself, dipping 

 at 26° north-westward. The grits are softer than their equivalents 

 to the westward. They are more argillaceous, and attain an indi- 

 vidual thickness of only 2 or 3 inches. The peculiar carbonaceous 

 Landing, however, leaves no doubt as to their exact horizon. 



The rock is dark grey, and weathers externally to dark brown 

 and metallic tints. The intercalated bluish-grey flags are evidently 

 false-bedded, and are striped with thin wavy sandstone and rotten- 

 stone bands. A few of the black seams yield Monograptus Clingani, 

 M. lobiferus, Dlplograptus Hughesii i Nich., and Climacograptus 

 normalis. 



At a short distance below the gate a fault crosses the lane. This 

 brings down the Gafallt Shales (j3& 2 ) which are exhibited in Nant- 

 y-Fuddai to the westward, extending for 100 yards down the brook. 

 West of this stream the ground is obscured by Drift, until the small 

 barn south of Fron-dorddu is reached ; and here the same sandstone- 

 banded shales are again displayed dipping at 22° north- westward. 

 In the lane to the farm, and in the farmyard itself, the first exposure 

 of the Bhayader PaleShales(C)is met with, these shales being 

 faulted against the Gafallt Shales a few hundred yards to the south. 

 They closely resemble the rocks of the underlying group, but the 

 chief distinction lies in the total absence of arenaceous banding. 



(4) Dol-Ifor. 



Beturning to the conglomerate-beds at Pen-y-rhiw, we may 

 follow them as they swing round in a sharp curve to the northward. 

 The Upper Conglomerate (Ba 3 ) ends at about 50 yards above 

 the boundary-hedge, and the Lower Conglomerate (Ba x ) at the 

 hedge itself, where it has a thickness of barely 50 feet. If the 



