674 KEPOKT— 1886. 



of interstratified shale, containing numerous fossils, including Produeliis giganteus 

 and corals. Thickness, 500 feet. 



Middle White Limestone. — A wlilte or light-grey thick-bedded limestone, con- 

 taining very few fossils. Thickness, 600 feet. 



Lower Broion 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 remams of plants. Thickness, 400 feet. 



The total thickness of these four subdivisions, forming the carboniferous lime- 

 stone of the north of Flintsbire, is 1,700 feet, which is much greater than anywhere 

 else in North Wales. 



Although the line of the section is nearly north and south, the average dip of 

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

 N.E.N, at Moel Hiraddug, so that it is greater than it appears to be in the section. 

 The highest subdivision, the Upper Black Limestone, occurs at the north end, and 

 the Upper Grey Limestone crops out from under it and extends to Nant-yr-Ogof, 

 where there is a considerable fault, which brings up the top of the Lower Brown 

 and the base of the Middle White Limestone. From the fault the Middle White 

 extends three-quarters of a mile, when the Lower Brown Limestone crops out, 

 continues some distance and forms the conspicuous hill, Moel Hiraddug, on the top 

 of which the lower beds of the Middle White Limestone are again exposed. 



Along the west and parallel with the section there are two great faults, known 

 as the Prestatyn fault and the Vale of Clwyd fault, and on the western side of the 

 former a bare limestone liill, Graig-fawr, rises to an elevation of 500 feet and 

 presents a grand exposure of the Middle Wliite Limestone, which is 600 feet in 

 thickness. Numerous fossils occur at the north end of Graig-fawi", and a greater 

 number has been obtained there than from the Middle White Limestone anywhere else. 



On the west of the carboniferous limestone shown along the hue of section 

 several faults, including the two already referred to, have thrown down the lime- 

 stone beneath the level of the sea, and the Lower Coal-measures have been proved 

 to occur at Meliden and Dyserth, beneath a covering of drift. In one of the recent 

 'Memoirs of the Geological Survey,' by Mr. A. Strahan, M.A., F.G.S., a full 

 description of the geology — Explmiation of Quarter-sheet 79 N. W. — will be found, 

 with all the details of the drift and underlying strata. 



7. On tlie Classification of the Carhoniferous Limestone Series : 

 brian Type. By Hugh Miller, F.E.8.E., F.O.S. 



It is now twenty years since the late George Tate, of Alnwick, published a 

 completed classification for the Carboniferous Limestone Series of North North- 

 umberland. For more than half that period this classification has been set aside 

 as of a merely local value. It will be the endeavour of this paper to claim for it 

 its true place. 



Tate's classification may be summarised as in the following table : — 



Carboniferoxis Limestone Series op North Northxtmberland : Tate's 

 Classification, 1856-1868. 



Upper or Calcareous group : — Fro7n the base of the Millstone Grit to the Lhin 

 Limestone — ' the lowest limestone of any value.' Good workable limestones, 

 interstratified with alternations of sandstone, shale, and coal ; large numbers 

 of marine organisms connected with the calcareous strata. Thickness, about 

 1,700 feet. 



Lower or Carbonaceous group : — From the base of the Dun Limestone to the top 

 of the Tuedian group. Marked by the number, thickness, and quality of its 

 coal seams ; limestones thin and generally impure ; marine organisms in fewer 

 numbers. Thickness, 900 feet. 



Tuedian group : — Beds intermediate hetiveen the productal and encrinital lime- 

 stojies and the Upper Old Red Sandstone. Distinguished by coloured shales, 

 by thin, argillaceous and cherty or magnesian limestones, and by the rarity of 

 encrinites and Brachiopoda ; some Stigmarian layers, but no beds of coal. 

 Thickness, about 1,000 feet. In one of his papers Tate distinguishes an 

 upper group of ' Tuedian grits.' 



