Page:VCH Rutland 1.djvu/37

 GEOLOGY In Rutlandshire these sands comprise beds of sandy ironstone at the base (from 6 to 1 2 feet thick) which pass up through brown ferruginous sandstone and brown sand into fine white sand with thin layers of grey clay and lignite ; these upper beds are from 10 to 20 feet thick and are known as the Lower Estuarine Series. The main outcrop of the Northampton Sands enters Rutland near Barrowden in the valley of the Welland and forms part of the ridge which runs northward by Morcott and LufFenham to Whitwell, Burley and Market Overton. There are however some extensive outliers to the west of this line, one large irregular outlier forming the ridges which extend from Seaton and Morcot to and beyond Uppingham ; others occur round Ridlington, Pilton, Manton and Hambleton. The sands are everywhere a source of water-supply (see p. 13), and springs occur at frequent intervals along their line of outcrop. The ironstone, when quarried at some depth from the surface or traversed in sinking wells, is a hard compact rock of a blue or greenish colour, consisting mainly of carbonate of iron and largely composed of small round grains which are formed of concentric layers, so that the rock has an oolitic structure. Near the surface however it has been oxidized and altered by the percolation of water, so that it presents a very different aspect, being then a brown porous or cellular rock consisting entirely of hydrated peroxide of iron. The transition from the one aspect to the other can sometimes be seen in a deep quarry, for at some depth from the surface each block of stone will be found to contain a centre of grey or bluish carbonate of iron, and still lower down there is more of the blue and less of the brown ironstone in every block, till at last the whole mass consists of the carbonate, which is solid and heavy, while the brown ore is light and is called ' kale ' by the quarrymen and well-sinkers. Near Uppingham and also at some other places the lowest beds are more calcareous and less ferruginous than those which overlie them, and have been extensively quarried for building purposes ; at Uppingham there is from 6 to 8 feet of such stone. Where the rock is oxidized the fossils have been destroyed, but in the blue rock shells are sometimes abundant ; they are almost all of marine genera, and the commonest are Ammonites Murchisona^ Belemnites gtganteus, the bivalves Astarte elegans, hucina Wrighti, Ceromya bajociana, Pholadomya Jidicula, and the sea-urchin Pygaster semisulcatus. These fossils show that the rock represents the lower part of the Inferior Oolite of the south-west of England, namely the zones of Ammonites opalinus and A. Murchisonce. In the overlying sands fossils are rare, but shells of Cyrena have been found in some places, and plant remains with vertical casts of their root- lets are not unfrequent ; moreover the thin layers of lignite have been formed by the decay of vegetation, and each layer is underlain by a thin seam of clay, just as in the Coal Measures beds of coal are generally underlain by beds of clay. It is clear that the whole group of beds was 5