Page:VCH Warwickshire 1.djvu/36

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A HISTORY OF WARWICKSHIRE neighbourhood of Nuneaton. They consist of a lower sandy division, the Hartshill Quartzite, and an upper shaly division known as the Stockingford Shales. In 1829 they were classed by Yates ' as of Silurian age, on account of the resemblance of the quartzite to that of the Lickey Hills near Bromsgrove. Subsequently however they were put into the Carboni- ferous system; 1 the Stockingford Shales, which seemed to be perfectly conformable with the overlying Coal Measures, were thought to be an unproductive group of that formation, while the Hartshill Quartzite was held to be a metamorphosed representative of the Millstone Grit. No fossils had then been obtained from either of the two divisions, and some of the shales have a decided coal-measure aspect. It is evident however that Jukes 3 recognized their Silurian or even pre- Silurian age. But the discovery in 1882 by Professor Lapworth * of a number of fossils in the Stockingford Shales characteristic of the Lingula Flags of the Upper Cambrian (then classed as Lower Silurian by the Geological Survey) finally settled the age of the higher of the two sub-divisions ; and in confirmation of these discoveries the revised issue of the Survey map in 1886 represented the Shales and with them the Quartzite as Lower Silurian. It still remained desirable to determine on independent evidence the age of the Quartzite. This has since been rendered clear by the recent discovery in its higher beds of a fauna highly suggestive of the O/ene//us-zone of the Lower Cambrian of other regions ; and as Professor Lapworth points out, ' it now appears exceedingly probable that the whole of the Cambrian system is represented here in an attenuated form.' 6 The Cambrian outcrop of Nuneaton extends from near Bedworth on the south-east to Merevale on the north-west, a distance of about eight miles, the greatest width being about a mile. The beds dip generally in a south-west direction at angles varying from 20 to 45, having been tilted up by crumpling of the earth-crust at some time subsequent to their deposition. The upper beds pass unconformably under the Coal Measures of the adjacent coalfield, while the lowest beds rest unconformably on the Archaean rocks already described. From base to summit the beds are pierced by dykes and sills of intrusive diorite (camptonite), and the whole outcrop on account of the relative durability of the rocks forms a low ridge of picturesque and wooded country. The rocks are divisible in the following manner, in descending order: 1 Tram. Geol. Soc. ser. t, ii. 237.

  • Geol Survey map, 63 S.W. (1855); also Howell, The Warwickshire Coalfield,' Mem. Geol.

Surrey (1859), p. 8. 'The South Staffordshire Coalfield,' Mem. Geol. Survey, ed. 2 (1850), p. 134..

  • Geol. Mag. (1882), p. 563.

8 Pnc. Geol. Atioc. xv. (1898), 338. 6