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Section across Moel-v-garth. 

 (Section I, fig. 1.) 



The succession can be best established 

 by a brief description of the two most 

 typical sections in the area. A fairly 

 complete succession may be obtained by 

 starting at the foot of the dingle by 

 Penbryn Farm and working in a south- 

 westerly direction towards Cloddiau, 

 Ty-brith, and Trefnant. It will after- 

 wards be necessary to deal with each 

 subdivision in detail. 



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Trilobite-Dingle Shales.— The 

 stream by Penbryn Farm has cut a 

 narrow gorge in a mass of dark-grey 

 splintery shales. The weathered surfaces 

 are usually stained reddish-brown or 

 yellow. The upper beds near the road 

 that crosses the top of the dingle consist 

 of more massive mudstones, which pre- 

 sent a nodular appearance when broken. 

 About 800 feet of these beds are here 

 exposed. 



Pwll-y-glo Group. — As we pass 

 along the road to the south-west, shales 

 and mudstones soon give way to beds 

 which differ, in that they are banded 

 with flags as well as with occasional 

 seams of grit. They can be traced in 

 the road, and are exposed in an old 

 quarry on the south side of it : about 

 300 feet of these strata are passed here. 

 This group is intermediate in character 

 between the underlying shales and the 

 overlying grits. 



Gaerfawr Group. — On our right 

 we now face the fine tree-covered ridge 

 of Moel-y-garth, which is an escarpment 

 formed by the outcrop of hard massive 

 grits. These grits are now seen crossing 

 the road : they are in thick beds, with 

 some shaly parting below and sandy 

 flags above. Between 700 and 800 feet 

 of these beds are passed over — the full 

 sequence not being shown, owing to the 

 overlapping of a massive red conglo- 

 merate. 



in 



Powis-Castle Group. — This con- 

 glomerate crosses the road about 150 



