120 Notices of Memoirs — Carboniferous Limestone of N. Flintshire. 



Tate's admirable classification presents us with well-defined types, 

 generally recognizable almost at a glance by the practised eye, and 

 bounded by lines as good probably as from the complications of the 

 structure (faults, obscurities, etc.) could be expected. His names, if 

 not high-sounding, are at least sufficiently expressive. 



II. — The Caeboniferous Limestone of North rLESTTSHiEE. By G. H. 



MORTOK, F.G.S. 

 (Abstract of Paper read before the British Association, Birmingham, September, 1886.) 



IN the year 1870 I described before the Association the subdivisions 

 into which the Carboniferous Limestone of North Wales is 

 naturally divided by clear lithological characters, and in 1877 more 

 fully described the subdivisions of the formation as they occur in the 

 Egiwyseg ridge, near Llangollen. Since then the whole of Flintshire 

 has been examined, and the original classification found to extend to 

 the sea-coast at the north of the county. Although the subdivisions 

 are not piled up, one over the other, in a precipitous outcrop, the 

 succession is as clearly shown between Prestatyn and Meliden as at 

 Llanymynech and Llangollen, and the uniform character of each sub- 

 division along the ititervening 44 miles of country is remarkable. 



The following four subdivisions of the Carboniferous Limestone are 

 all well exposed in a fine mural section 3^ miles in length, from Castell 

 Prestatyn on the north to the end of Moel Hiraddug on the south, and 

 occur in the following descending order : — 



Upper Black Limestone — a black, fine-grained, thin-bedded lime- 

 stone, containing very few fossils, but including Posidonomya Becheri 

 and the remains of many plants. Thickness, 200 feet. 



Upper Grey Limestone — a dark grey, thin-bedded limestone, with 

 thin seams of interstratified shale, containing numerous fossils, including 

 Productus giganteus and Corals. Thickness, 500 feet. 



Middle White Limestone — a white or light grey, thick-bedded lime- 

 stone, containing very few fossils. Thickness, 600 feet. 



Lower Brown Limestone — a brown or dark grey, irregularly -bedded 

 limestone, containing few fossils, but with interstratified shales at the 

 base of the subdivision, which contain the remains of Plants. Thickness, 

 400 feet. 



The total thickness of these four subdivisions, forming the Carboni- 

 ferous Limestone of the North of Flintshire, is 1700 feet, which is much 

 greater than anywhere else in North Wales. 



Although the line of the section is nearly N. and S., the average dip 

 of the strata is about 14° to the E.N.E. at Coed-yr-Esgob, N.W. at 



which crops out for some miles along the coast at Lamberton . . . But in the Upper 

 Coquet district (Mid- Northumberland), where the Tuedians are extremely well 

 developed, no such limestone can (could) be traced, and the Harbottle Grits are so 

 thoroughly Bernician in facies, and so well divided stratigraphically from the 

 Tuedians, that there the base of this great sandstone series forms quite the most 

 convenient boundary-line. Now there is little doubt that the horizon of the 

 Lamberton or Dun Limestone is above the Harbottle Grits, so that the merely 

 expedient and artificial character of the boundaries thus arrived at is shown at once. 

 The truth is that no line should be drawn at all except as the merest matter of 

 convenience." — Lebour, Outlines of the Geology of Northumberland, p. 44. In the 

 diagram it is of course a matter of convenience that this confessedly artificial limit 

 should be represented by a dotted line. 



