390 ME. G. H. MORTOIS' 01^ THE CAEBONIFEEOITS [Aug. 1898^ 



A list of the fossils found in the Middle White Limestone is appended 

 (see pp. 392-393). They were all found in the 7 feet of black shale 

 at the base, or in the limestone within 20 feet above it, with the 

 exception of Bellero^hon costatas, Edmondia sulcata^ and Cytherella 

 cequalis, obtained from about the middle of the subdivision. 



(3) Upper Grey Limestone. 



The Upper Grey Limestone is the highest subdivision of the 

 Carboniferous Limestone. It occurs on the top of Great Orme's 

 Head, occupying an elliptical area of about a mile from east to west, 

 and half that from north to south. It covers a depression in the 

 Middle White Limestone, and has a general dip towards the centre. 

 The base on the south-east is a thick bed of grey shale, clearly 

 exposed at the top of the ' Old Hoad ' from Llandudno, about 

 450 feet above Ordnance datum, and the following is a section of 

 the beds : these dip about 10° N.W., but they are well exposed only 

 on the strike ; — 



Ft In. 



Thin limestone 1 6 



Grey shale 6 



Impure limestone 2 



Grey shale 9 



18 6 



Fossils are numerous in the shale, and include Orthis MicheUni, 

 Productus giganteus, Pr. longispinus, Spirifera hisulcata, Sj^- Uneata, 

 and Terehratula hastata. The shale may be traced along the sur- 

 face of the ground for about 100 yards to the westward, where it 

 becomes covered with debris from the old mines ; but it does not 

 seem to be at the base of the subdivision for a much greater dis- 

 tance. In the absence of the thick shale, the lowest strata consist 

 of thinly-bedded black limestone in bands about a foot in thickness, 

 interstratified with black shale from 9 to 12 inches thick, both 

 being well exposed in a series of quarries 300 yards south of the 

 Telegraph. Along the outcrop of the lowest beds in other places 

 the Upper Grey Limestone consists of thin beds of black limestone 

 with little shale between them. The limestone worked in the 

 quarries is about 40 feet thick, and is taken down to Llandudno and 

 used for rough building purposes, instead of that formerly obtained 

 from the base of the Middle White Limestone, which it resembles. 

 The dip of the beds is 15° N., and the limestone is crowded with 

 Productus giganteus, thousands of which may be seen of all sizes, 

 while in the shale Pr. margaritaceus, a rare species in other localities, 

 is very abundant. Many other fossils occur : these are tabulated in 

 the appended list, pp. 392, 393. Athyris ambigua is a rare variety 

 figured by Davidson.-^ 



^ Suppl. ' Oarb. Brachiopoda,' Monogr. Palasont. Soc. p. 283, pi. xxxiv, figs. 10 

 & 11. 



