Page:VCH Warwickshire 1.djvu/48

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A HISTORY OF WARWICKSHIRE Wilmcote they were excellently exposed in quarries as described by Wright ; the White Lias consisting of hard crystalline limestone, below which follow marls and blackish shales with Estheria minuta and the characteristic Avicula contorta and Pecten -valoniensis. A bone bed has been noted at Temple Grafton. Strickland recorded the presence of black shales and yellow sandstone at Bidford, and Brodie 1 has given details of the sections exposed on the Stratford and Fenny Compton railway. The railway section of the Rhstics and Lower Lias at Har- bury, south-east of Leamington, has long been famous ; the yellow sandstone with Estheria minuta is present below the White Lias. Still farther along the base of the Lias the Rhastic beds have been exposed on the London and North- Western railway west of Church Lawford near Rugby ; according to Mr. Woodward 2 they consist of 5 or 6 feet of buff limestones overlying 5 to 8 feet of greenish-grey marl ; the Avicula contorta shales appear to be unrepresented. Brodie 3 described two interesting outliers or small isolated patches of Lower Lias and Rhastic beds south-west of Henley-in-Arden, and another, still farther away from the main tract, at Knowle. The Rha;tic beds of these outliers have yielded some of the usual characteristic fos- sils. The Knowle outlier which is situated some 10 miles to the north of the main Liassic tract is interesting as showing the former extension of these beds in a northerly direction ; Dr. Lloyd of Leamington seems to have been the first to detect its existence. The Lias limestones were formerly wrought by shafts. The Rhstic shales contain a band of yellow micaceous sandstone with the fossil bivalve Pullastra arenico/a, and were noted by Brodie as exposed in the banks of the canal. From the foregoing details of the Warwickshire Rhaetic beds it would appear that they do not present anything like the full develop- ment as exhibited in the classic sections of Penarth or Aust on the shores of the Bristol Channel ; as Mr. Woodward * points out, ' there is a development of sandy beds, the black shales are very thin in places, and near Church Lawford they are absent; again, the White Lias north of Harbury is somewhat sandy, it shows current-bedding and ripple-marks, and is itself occasionally nodular,' and he concludes that the beds of our district were laid down not far from a local margin of the deposit. By the end of the Keuper Marl period the general subsidence of the whole British area which had been going on from the close of the Bunter epoch had resulted in the submergence of the barriers which had hitherto kept out the sea; this now gained access to our district, and with it the period of the desert and lacustrine Red Rocks came to an end; and henceforward marine deposits alone were laid down over the site of the future Warwickshire. As we have seen, the first of these consists of the Rhatic limestones and shales which serve merely as an introduction to the Lias. ' Quart. Journ. Gtol. Soc. XH. (1874), 746. Op. cit. p. 162. Quart. -Journ. Geol. Soc. xxi. (1865), 159. < Op. cit. p. 151. 18