D. C. Davies — T/ie Millstone Grit of North Wales. 



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wood, we find tlio junction of tin's with the liuiostono proper (See 

 Woodcut, Fig. 2). The section, however, which best ilhistratcH this 

 point, is seen in a small and comparatively unknown quarry at 

 Carreg-y-big, 3^ miles north of Oswestry (See Woodcut, Fig. 3), 

 where we have at the base the limestone proper, which is here burnt 

 for Agricultural use, and at the summit thin sandstones of the Mill- 

 stone Grit. It will thus bo seen, that the cliange in the character of 

 the deposits, while it was somewhat gradual, was, in the southern 

 part of the area in question, marked and permanent. There were 

 temporary cessations of the supply of calcareous matter, at various 

 periods during the deposition of the Carboniferous Limestone, as is 

 evidenced by four or five well-marked ferruginous shaly beds in the 

 lower, and of bituminous shales in the upper portion of that 

 formation ; the supply of calcareous matter became subsequently less 

 and less, and, with the exception of an unimportant outflow in the 

 middle beds, permanently ceases. These remarks are however only 

 applicable to the southern half of the area, as I shall have occasion 

 to explain presently. 



Fig. 1.— Section of Millstone Grit at Sweeney, 2^ miles South of Oswestry, 



s e 7 



1. Carboniferous Limestone : Productus, Lithosfrotion, and usual fossils of the top beds. 



2. Covering of Drift, hiding the junction of the Limestone with the Grits. 



3. Yellowisii ferruginous sandstones, massive dark red ditto with coarse pebbles. Fossils in some 



of these beds; Corals, uncertain species; Rhynchonella, Sanguinolites, Metoptoma, 

 Chonetes, Productus semireticulatus, P. cora, etc., etc, 



4. Calcareous sandstones, about 60 feet. 



5. Soft, white, buff, mottled, and striped sandstones, with thin beds of marl and shale. Schizodus 



in some of these beds. 



6. Fine-grained hard pale sandstones, with occasional layers of pebbles, and, in the fine beds, 



reticulated plant and annelide-markings. 



7. Beds of friable sandstone, passing upwards into solid beds of pinky-white sandstones, with 



lateral pockets, capped with thin beds dipping under the Coal Measures. Productus 

 semireticiilattis in great abundance, large Orthoceratites, Catamites, and fucoid remains. 

 Total thickness of Grits between the Carboniferous Limestone and Coal Measures, 282 feet. 



8. Coal Measures. 



Fig. 2.- 



-Section showing the junction of the Millstone Grit with the Carhoniferous 

 Limestone, in Craigforda Wood, 3 miles N.N.W. of Oswestry. 

 E,iver Morda. 



1. Carboniferous Limestone, covered by, 



2. Light grey limestones, with brownish markings and stems of Encrinites. 



3. Thin bed of dark red marl. 



4. Calcareous sandstones with purplish markings. 



5. Thin beds of brownish sandstones with cavities — casts of concretions or fossils. 



6. Steep slope covered with sandstone blocks from the upper beds. 



