lo8 PHOF. T. T. 6E00M ON THE GEOLOGICAL [^^a}' ^^99) 



In the looality now under consideration the Black and Grey 

 Shales together form part of a fold the axis of which is directed 

 north-westward, and the north-eastern limit of which is overthrown 

 and faulted against the Hollybush Sandstone and Archaean (figs. 4-6 

 & 13, pp. 136, 144), while on the south-east the series is overridden 

 by the schists of Chase End Hill, and, at any rate in the southern 

 part of the district, inverted (fig. 16, p. 149). 



The best section in the district is that taken from the village 

 of White-leaved Oak, south-westward down a little valley running 

 between Pendock's Grove and Coal Hill (fig. 13, p. 144). 



The Hollybush Sandstone at White-leaved Oak forms a steep slope 

 on which many cottages of the village are situated (PI. XIV) : the 

 beds dip west-south-westward at a high angle. At the foot of the 

 slope the Black Shales are seen, often much disturbed and generally 

 inverted, so as to dip at an angle of 60° or more in a north- 

 easterly direction. The mutual dip of the sandstone and shales 

 towards one another can be explained only on the supposition that 

 the junction is a fault. 



A well-marked band of basalts interstratified with shales passes 

 through the village, forming a round-backed ridge, the central line 

 of which crosses the road immediately south-west of the village. 

 This band is tripartite, there being three minor bands chiefly com- 

 posed of basalts, separated by two thinner bands made up essentially 

 of Black Shales. 



The Black Shales on the north-eastern side of this igneous band 

 have an inverted north-easterly dip, as seen in the fields north 

 of the village. Those interstratified with the basalts are almost 

 vertical, and those overlying the igneous band have a very high 

 south-westerly dip. Traced south-westward, the Black Shales are 

 last seen at the northern corner of Pendock's Grove. Beyond this 

 point the Grey Shales commence, and at their base are interstratified 

 with basalt. This band, accordingly, forms a second well-marked 

 ridge, separated from the first by a considerable depression occupied 

 by Black Shales with little or no igneous material. 



Igneous materials seem to occur almost everywhere in the Grey 

 Shales along the rest of the line of section, but are specially developed 

 only along a third ridge, passing through the middle of Pendock 

 Grove, and forming Coal Hill on the other side of the glen. Basalts 

 occur in the lower part of this band, but the chief igneous rocks 

 are ophitic diabases; these are well-exposed in the garden of the 

 cottage at the north-western end of Coal Hill. The interstratified 

 shales and diabases here dip south-westward at an angle of 35°. 



Between the western foot of the Coal Hill ridge and the May Hill- 

 Sandstone escarpment the Grey Shales can be traced along the 

 line of section by abundant debris only, and the determination of 

 the exact position of the junction of the shales with the Llandovery 

 Beds was a matter of difficulty, but was effected, I think, with 

 some approach to accuracy by the aid of excavations, and by noting 

 the upper level to which the shale-debris extended. 



In the extreme eastern corner of the district traces of another 



