352 



LOWER SILURIAN ROCKS. — NOETH-GRUG. 



Mwmfre Hills, we find that in the still higher ground around Noeth-griig (1500 feet 

 above the sea) they recover the true lithological character of the Caradoc sandstone, the 

 strata being loaded with the peculiar organic remains. These hills constitute the most 

 interesting tract in Caermarthenshire, since they exhibit a passage on the one side into 

 the Upper Silurian Rocks, and on the other into the Upper Cambrian. 



The central part of Noeth-griig is dome-shaped, with deeply indented steep escarpments on the 

 north-east, and slightly inclined slopes to the south-west, west, and north-west. On the south- 

 east it is flanked by the cliffs of Castell-craig-gwyddon and the low ridge of Gorllwyn, and on the 

 north-west by the sharp ridge of Cefn-y-garreg. The whole mass consists of sandy schist, sand- 

 stone, and quartzose grit, with sometimes a fine conglomerate. For the better comprehension of the 

 arrangement of the strata, I refer to the transverse section from the escarpment of the Old Red 

 Sandstone of Mynidd bwlch-y-groes, across the Silurian System, to the hills of Cambrian rock 

 on the north-west. (See PI. 34. f. 3.) The beds which first rise from beneath the dark schists 

 of the age of the Wenlock shale are grey quartzose grits, in parts a conglomerate, which mount 

 up into the bold cliff of Castell-craig-gwyddon and dip 75° to the south-east. The lower strata 

 are thick-bedded, and were formerly much quarried for building materials, a fact strongly in- 

 dicative of the absence of good durable stone in this country, seeing that it has been sought 

 in this rugged and inaccessible spot. The thinner and overlying beds are filled with casts of shells, 

 among which are Pentamerus ohlongus, P. Icevis, Orthis Actonia, &c, Spirifer liratus, crinoidal 

 stems with granulated surfaces, and several species of coral. 



A short anticlinal line ranges from south-west to north-east along the summit of this ridge, as 

 explained at its north-eastern extremity, where subsiding into a low hill, the strata dip both to the 

 south-east and north-west. The quartzose grits are also bent over in the chief hill of Noeth-griig, 

 where they undulate and dip in fan shapes to the west-south-west, west, and north-west, covering 

 an area of about four square miles. (See Map and PI. 34. f. 3.) The eastern and north-eastern 

 sides of these hills terminate with a steep escarpment, on the sides of which beds of schist and 

 argillaceous sandstone appear from beneath the harder sandstone. 



The north-western face of the Noeth-griig is marked by a number of hard, rocky, protruding 

 ledges of sandstone, which dip successively 25° and 30° to the north-west. Descending to the 

 westward into the depression between Noeth-griig and Cefn-y-garreg (PL 34. f. 3.), the same strata 

 are curved into small elliptical basins, as represented in the annexed wood-cut, 



Cefn-y-garreg. North-western slopes of Noeth-griig. 66, 



N.W. 



S.E. 



