228 MESSES. T. C. CANTRILL AND H. H. THOMAS ON THE [May 1906, 



reappear at Glog Farm, where they may be seen near the well a 

 few yards north-east of the house. They consist of felsite-con- 

 glomerates and interbedded black shales which have yielded Orthis. 



Traced westward from Glog, the grit-crop extends for about half 

 a mile to the cross-roads north of Pen-gelli-uchaf. It is bounded 

 on the south by a faulted strip of ground, which includes the 

 rhyolites of Capel Bethesda, and a remarkable rhyolite-conglome- 

 rate of doubtful age. At the cross-roads is a quarry in rotten 

 diabase, which appears to have been intruded into the grits. 



The bare surface of the road about 60 yards north of the cross- 

 roads shows pebbly grits, largely made up of rhyolite, within a few 

 feet of the diabase which is exposed on the road-surface and also 

 in the old quarry hard by. The grit-outcrop can be followed from 

 this point as far as the site of Lan-ganol, 120 yards south of which 

 a small quarry by the side of a field-road shows, within a few 

 feet of the conglomerate, black, yellow-weathering shales. These 

 yielded Dictyonema sp. and Orthis Actonicv (?) Sow., and appear to 

 be identical with the shales which immediately succeed the conglo- 

 meratic grits in the Caermarthen district. 



At Lan-ganol the grit-outcrop abruptly turns back on itself, 

 and trends in a west-south-westerly direction. At Pen-y-graig 

 Farm it forms a prominent elliptical hill, on the north side of 

 which a roadside-quarry, 80 yards west of a ruined windmill^ 

 exhibits massive pebbly grit apparently dipping northward at 70°. 

 It has already been pointed out (ante, p. 224) that Murchison's 

 map represents a patch of trap somewhere hereabouts, but we 

 have not been able to find any such rock. 



South-west of this quarry are several exposures of the grits and 

 conglomerates in the roads, by which the outcrop can be traced to 

 Ffald. Here it appears suddenly to terminate against a north-east 

 and south-west fault, which introduces an outcrop of higher non- 

 conglomeratic grit. 



The conglomeratic grits reappear, however, in Pen-y-Moelfre. 

 This hill consists of an elliptical mass of grits and conglomerates ; 

 it seems to be faulted on all sides, except on the west-north-west r 

 where the grits appear to pass up into shales. It presents good 

 sections by the roadside south of Llangynog School, and a few 

 yards farther south at some roadstone-quarries, where the beds are 

 vertical. 



At the southern end of the hill, about a quarter of a mile farther 

 to the south-east, a large quarry near Llangynog Yicarage shows 

 coarse buff sandstone, with frequent pebbles and some shale- 

 partings ; the grits have yielded Orthis. Here it is very evident 

 that they are cut off on the south by a fault, for they strike 

 directly towards a good section of fine-grained olive-green shales 

 and sandstones, much disturbed and contorted, at the Vicarage- 

 gates. 



East of this section the grits make up the lofty hill of Moelfre 

 Wood, and are exposed in the road at Moelfre Gate. The hill ends 

 in a bold north-and-south scarp a little west of Moelfre Farm, and, 



