LOWER SILURIAN ROCKS — CAERMARTHENSHIRE. 



351 



The hill of Goleugoed has hitherto proved richer in organic remains than any other 

 portion of this tract, but all the strata lying between Llandovery and Llangadock are 

 so disturbed and affected with reversed dips, that it is difficult to separate the younger 

 from the older strata with precision. At Blaen-y-cwm, near Sardis chapel, dark sandy 

 grits are heaved into vertical positions, flanked by schist and dark grey, white-veined 

 quartzose sandstone, striking from south-east to north-west. In these grits were found 

 some fine specimens of Nautilus undatus. (PI. 22. f. 18.) Again, near the summer-house 

 on the point of the hill of Glas-alt-fach is thin-bedded, bluish grey, slightly micaceous 

 sandstone, dipping to the north with a strike from east to west ; whilst at the western 

 end of the hill, near the high road, coarse quartzose grits of the same character dip 45° 

 S.S.E. and strike N.N.E. and S.S.W. (See Map.) There is no doubt, however, that 

 these hills belong to the Caradoc sandstone, for they contain many remains peculiar to 

 that formation in the quarries at Rhiw-felig, LI wyn-y- wormwood, Cefn rhyddan, Go- 

 leugoed, &c. 



Many well known Caradoc fossils are mixed with some other species which I have not observed 

 in Shropshire or Montgomeryshire. Among these fossils, figured in PI. 19, 20 and 21 are Orthoceras 

 bisiphonatum* , Turbo PrycecE*, Buccinum angulatum, Turritella cancellata, Terebratula pusilla, 

 T. l*J-plicata*, T. tripartita, Pentamerus Icevis, P. oblongus, Orthis protensa, O. lata, O. radians, 

 O. aperturata, O. bilobata, Spirifer plicatus, S. liratus, Atrypa crassa, A. acuminata, A. lenti- 

 cularis, A. globosa, A. plana, A. orbicularis, A. undata, Productus depressus (var.), P. sericeus, 

 P. sericeus (var.), Orbicula granulata, Sec. (Those marked * have not been found in other locali- 

 ties.) 



The Llandovery building- stone has not generally the firmness and durability of the 

 Caradoc sandstone, being so loaded with argillaceous matter that if not speedily used 

 and cemented in a horizontal position, it decomposes like the "greenstone" of the 

 Upper Silurian Rocks of Shropshire, Montgomery, and Radnor. We thus see that the 

 two groups at distant points have completely changed their lithological characters, for, 

 as already remarked, p. 190, 204 et seq., the Upper Silurian Rocks, which in Salop 

 are more or less incoherent mudstones, are here brittle, compact sandstones, whilst 

 the hard Caradoc sandstone of Salop has passed into incoherent schist. But as if to 

 torment the unfortunate observer who would draw inferences from lithological struc- 

 ture, there are still striking exceptions to this rule. We have stated that at the south- 

 western end of these undulating hills (at Glas-alt-fach) the beds become hard, quartzose, 

 and slightly conglomerated, and if we follow them to the north-east, through the 



stone has been chiefly established through the zealous cooperation of Mr. Williams, surgeon of Llandovery, and 

 his son Mr. Stewart Williams, who have collected fossils from all the adjoining quarries, wherever a trace of 

 them could be detected. From his acquaintance with the Welsh language, and his intimate knowledge of the 

 topography and history of his native country, Mr. Williams has been enabled to render me most valuable assist- 

 ance. I have named the prominent fossil shell (found in the tilestone of Cwm-dwr by my able friend) Turbo 

 Williamsi, PI. 3. f. 6, as a slight tribute of respect and regard. 



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