Page:VCH Warwickshire 1.djvu/38

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A HISTORY OF WARWICKSHIRE The Lower or Purley Shales are exposed in Purley Park Lane and in the cutting on the Midland Railway near Nuneaton. The beds are generally reddish-purple and contain manganese ores which were worked by pits at various points along the outcrop. Fossils have been obtained from the Purley Park Lane sections, and include among others minute forms of the brachiopods Lingu/a, Obolella sagittalis, and Acrothele granu- lata ; the sponge Protospongia fenestrata, and the trilobite Conocoryphe exulans. The Middle or Oldbury Shales are best seen in the Midland Rail- way cutting at Stockingford, and in quarries and cuttings at Chapel End. The beds are characterized by black carbonaceous bands. They have yielded remains of the trilobites Agnostus pisiformis var. soda/is, Olenus nuneatonensis, Sphczrophthalmus a/atus, and Ctenopyge pecten ; together with Beyricbia angelini. The Upper or Merevale Shales are exposed in an old quarry 200 yards west of Merevale Abbey. They consist of greenish-grey shales and have yielded numerous examples of the hydrozoan Dictyonema socials. A small inlier of the Stockingford Shales was detected at Dosthill, south of Tamworth, by Mr. W. J. Harrison ' in 1882. The rocks are pierced by a mass of diorite. Sections in the shales have been recorded* as occurring in the side of the high road a quarter of a mile south of Dosthill, and in a small pit near Stockall Barn. The beds dip south- west at 20 to 40, and consist of highly-altered grey and olive-coloured sandstones. The following table shows the probable relationships of the Nun- eaton Cambrian beds to those of other districts : Nuneaton. Wales, etc. Merevale Shales Upper Dolgelly (Dictyonema-beds) ) TT T . Oldbury/ upper Lower Dolgelly ..... . / U PP er L" 1 ^ FIa g Shales I lower) II ga j| ~ [ g ,. Purley t upper/ Ffestmlo g and Maentwrog beds . Lower Lingula Flags Shales! lower ........... Menevian (Paradoxides--zone) Camp Hill Quartzite and Limestone . . 0/enel/us-zone Tuttle Hill Quartzite (Park Hill Quartzite The Cambrian rocks of Nuneaton afford evidence of having been deposited in a shallow sea whose floor was gradually undergoing subsi- dence. The quartzites and sandstones were perhaps to some extent shore deposits laid down at no great distance from a tract of land. This must have consisted in part of the Archzan volcanic ashes, for we have seen that much ground-down volcanic material was incorporated in the lower beds of the Hartshill Quartzite. As the sea bottom sank, the land, wherever this was situated, was gradually submerged, and the coarse ' Lapworth, Gtol. Mag. (,882) p. 563 ; Harrison, Mid. Nat. vol. viii. (.885) and vol. i*. (.886). ' Strahan, Geol. Mag. (1886), p. 551. 8