188 MISS G. L. ELLES ON THE RELATION OP THE [May 1909, 



drawn near the top of the Cadnant Shales ; while that between 

 the Ashgillian and the Valentian may eventually prove to lie in the 

 middle of the Conway Castle Grits. With regard to these last, all 

 that appears certain is that the upper part of them represents part, 

 at any rate, of the Hirnant Limestone, and that this upper part, 

 since it passes laterally into beds with a characteristic assemblage 

 of Lower Llandovery graptolites, must be regarded as being of 

 Lower Llandovery age. Whether or not the lower grits with their 

 associated unfossiliferous shaly beds should also be regarded as 

 representing the Hirnant Limestone ; whether they are the equi- 

 valents of the Slade Beds of South Wales, or of the Phyllojwra-'Beds 

 of the Lake District ; or whether these two also represent part of 

 the Hirnant Limestone, must be left for future work to decide. 

 There appears to be, at present, no definite evidence on this point 

 at Conway. 



South Wales. — With regard to the lower beds, the resemblance, 

 as a whole, of those of the Conway District to those of South Wales 

 is distinctly striking. The shales in the Yoleanic Series contain 

 the same characteristic graptolite as the Llandeilo Flags, and the 

 Cadnant Shales correspond precisely with the beds termed the Upper 

 Dicranograptus-'Shdles by the officers of the Geological Survey 

 (' Summary of Progress for 1907 ' 1908, p. 39.) 



The greater part of the Bodeidda Mudstones seem to correspond 

 with the Sholeshook Limestone, since they contain Trinucleus 

 seticornis down to their very base ; and the Deganwy Mudstones 

 are closely comparable with the Bedhill Beds. 



The upper beds, on the other hand, seem to find their closest 

 parallel in the succession at Rhayader and Tarannon, as described 

 by Dr. H. Lapworth l and Mrs. Shakespear. 2 



Bhayader. — At Rhayader, it would seem that the upper part 

 of the Conway Castle Grit is possibly represented by the Cerrig- 

 Gwynion Grit, the flags with Mesograplus modestus by the Dyffryn 

 .Flags and part of the Ddol Shales, while the shales of the Zone of 

 Monograptus gregarius are to be correlated with the upper part of 

 the Ddol Shales and the Gigrin Mudstones. The higher shales with 

 Monograptus sedgivicki correspond with the Gafallt Beds, and the 

 rest of the Gyffin Shales are represented by the Bhayader Pale 

 Shales, in part at any rate. 



Tarannon. — In the Tarannon country the comparison is even 

 closer, the most noteworthy differences being the absence of a 

 lithological type resembling the Conway Castle Grits at the base, 

 and the fact that at Conway there are no grit-beds corresponding 

 with the massive Talerddig Grits of the Tarannon area, that horizon 



1 Quart. Journ. Geol, Soc. vol. lvi (1900) p. 67. 



2 Ibid. vol. hrii (1906) p. 644. 



