Vol. 67.] ASSOCIATED ROCKS OF NORTH-EAST MONTGOMERYSHIRE. 



43: 



and these are indicative of Wenlock age, Pentamerus linguifer 

 being most common. The exposure is very small, but it is interesting 

 to find the Wenlock-Limestone facies extending to this district. 

 The bed is only 2 or 3 feet thick, and may be merely a local deve- 

 lopment; it is very similar, however, in its lithological peculiarities 

 ito the Wenlock Limestone of "Wenlock Edge. 



Eig. 5. — Map illustrating the exposures in Cwm Caeihro. 



(Western facies). — Passing from the eastern side of the district 

 over the anticline of Guilsfield Valley to the west, we find a most 

 interesting outlier of Wenlock Shales resting directly uponGaerfawr 

 Beds at Tyn-y-lhvyn, near Little Pwll-y-glo. 



The graptolite fauna shows that shales of the zone of Cyrto- 

 graptus lundgreni were deposited over the anticline, contrasting 

 with the Llandovery conglomerates which thin out over it. It is 

 evident, therefore, that a folding movement had already commenced 

 before the deposition of the Llandovery Series ; and a ridge of 

 Gaerfawr Beds, which are thin here and have evidently been much 

 denuded, formed an island in Llandovery times. This ridge was 

 finally submerged in the Upper Wenlock period ; and it will be seen 

 that the submergence was finally more complete in Lower Ludlow 

 times, since the Upper Wenlock Beds along with the Llandovery Beds 



