260 MR. W. GIBSON ON- THE CHARACTER OF [May IQOI, 



subordinate, they also occur in the productive series. There is no 

 sign of a break between the productive and the barren series ; on the 

 contrary, they are closely allied palaeontologically, lithologically, 

 and stratigraphically in this region. The chief movements are pre- 

 Triassic and post-Carboniferous. 



The sequence of the higher Coal-Measures in Denbighshire, 

 South Staffordshire, and Nottinghamshire will now be briefly 

 described^ No attempt will be made to recognize the Black-Band 

 Series, as, in the absence of limestone and bands of Black-Band 

 ironstone, the strata are indistinguishable from the productive series. 

 Nor will the relation of the higher Coal-Measures to the under- 

 lying strata be touched upon, as this can only be satisfactorily 

 settled by systematic mapping and a more prolonged examination 

 than I have been able to make. 



III. Denbighshire, 



The Coal-Measures of North Staffordshire appear again from 

 under the cover of Triassic rocks in Denbighshire. During two visits 

 to the ground round Euabon, Wrexham, and to the east of Chirk, I 

 was able to find the representatives of the Keele, Newcastle, and 

 Etruria-Marl subdivisions, thus confirming the opinion as to the close 

 connection of the Pottery Coalfield with that of Denbighshire. 



B,ed marls are well shown in the banks of the Dee and its 

 tributary, the Ceriog, to the east of Chirk. In Pentre-isaf Ravine, on 

 the northern bank of the Dee, the grey limestone with Spirorhis and 

 Carhonia, as described by Mr. D. C. Davies, is visible: it evidently 

 lies n«ar the base of the marls. Lower down in the ravine, but 

 higher up in the marls, a bluish-grey limestone with Sjoirorhis and 

 Carhonia was found. In the banks of the Ceriog bands of green 

 grits lying in red marls are seen near the junction of Glyn Morlas 

 with the Ceriog. Mr. D. C. Davies has accurately noted the presence 

 of these bands, here and elsewhere in the neighbourhood. He 

 states ^ that ' the pebbles and fragments consist chiefly of Lower or 

 Cambro-Silurian rocks with their imbedded quartz, felspar, green- 

 stone, and porphyry, together with fragments of Wenlock Shale 

 and Carboniferous Limestone.' The increased coarseness of the 

 bands of grit compared with those occurring in the Etruria Marls of 

 North Staffordshire is explained by the fact that the Denbighshire 

 Coalfield lies near the margin of the coal-basin, Silurian strata 

 cropping out 5 miles to the west. 



The upper portions of the marls are exposed in Glyn Morlas, and in 

 a small ravine near Pentre they are seen passing up into a series of 

 grey sandstones and marls. At the junction a thin band of reddish 

 limestone, containing Carhonia and Antliracomya caldfera, is de- 

 veloped. This makes it almost certain that the underlying marls 

 represent the Etruria Marls of North Staff'ordshire, and that the 

 overlying grey sandstones are the equivalents of the Newcastle- 

 under-Lyme Series. This identification is confirmed on finding the 



^ Quart. Journ. Geol. Soc. vol. xxxiii (1877) p. 11. 



