72 D. C. Davies—The Millstone Grit of North Wales. 



it holds good of the formation generally. There are, however, local 

 variations, as might be expected, arising from local causes, which 

 affected the original mode of deposition ; as, for example, the degree 

 of intensity of the currents, and the nature and amount of the 

 materials. It may therefore be interesting to note a few of the local 

 changes that occur as we follow the formation northwards from 

 Sweeney. At the southern end of Cyrn-y-broch, north-west of Os- 

 westry, the beds corresponding to the upper 26 feet of the Sweeney 

 section are changed in colour to yellow, and becorae in their upper 

 portion very cherty and splintery. The uppermost beds, seen in a 

 quarry on the right of the road from Oswestry to Llansilin, near the 

 Eacecourse, become flaggy, and are covered with well-defined rip pie 

 marks. In the Forest quarry, on the north-west side of the Oswestry 

 Uacecourse, there is a bed corresponding with the pale hard fine- 

 grained sandstone of Sweeney, which becomes veiy coarse and 

 pebbly, and contains in its finer portions well-defined crystals of 

 felspar. Over this there is a bed, one foot thick, which is literally an 

 agglomeration of pebbles, covered by an irregular deposit of sand, 

 pebbles, and sandstones, about 3 feet thick. 



Section of Millstone Grit at Trevor, near Llangollen. 



[This pection was kindly given to me by the Messrs. Koberts, of Garth Quarry, Trevor, from a 

 record of borings made below their quarry, in the 78ft. of Sandstone at the head of the section.] 



Thin seam of Coal. — Base of the Coal Measures. Thickness, 



Compact Sandstone, -with crystals of folspar, varying in texture from a coarse con- ft. in. 



glomerate to fine grained sandstones used for building purposes ... 

 Dark grey clayey shale ... ... ... 



Grey flinty stone ... 



White shale 



Dark grey shale, with iron pyrites ... 



Hard white sandstone 



White clay and chert 



Black shale 



Hard cherty rock; decomposes into rotten stone 



Black shale 



Hard rock 



Black shale 



Hard rock 



Fire-clay... 



Ditto and sand 



Kock 



White Rock 



Brown ditto 



Dark shaly rock ... 



Black shale 



White rock 



Shale 



Limestone (metalliferous). [N.B.— Broke my chisel] 



138 3 



Section taken along the outcrop of the beds to the junction of the Grit with 



the Limestone. The figures must be regarded as approximately correct. 



White cherty limestone, in thin splintery beds, below a solid bed of limestone, 1ft. Gin. 



thick, corresponding with the base of section above 

 Massive white sandstones with pebbles, forms two ridges 



>, ,, ,, ,, forming a lower ridge 



Brown sandstones, a little calcareous, passing downward into a lighter colour of 

 Yellow and brown sandstones 

 Pink and white variegated sandstones 

 Calcareous sandstones 

 Yellowish white, with darker coloured ditto, with purple calcareous spots ... ... 3 



Thin flaggy buff and yellow sandstone beds, in places honeycombed by decomposition of 



mineral matter, as at Cragford and Bronygarth... ... ... ... ... 3 



resting on 



294 3 

 Pale limestone, few fossils, near the junction, but passing downwards into an enerinital 



and coralline limestone. Top of the main body of Carboniferous Limestone of the 



Eglwseg Kocks. 



78 











9 



4 







1 



3 



9 



3 



16 







6 











3 



5 







2 







2 



4 







3 



2 







2 







1 



8 







10 







2 



10 







10 







3 







4 



3 







1 



3 



16 







40 







27 







8 







4 







20 







35 







