Page:VCH Rutland 1.djvu/35

 GEOLOGY north-eastern corner of the county, though it occupies a large area in the adjoining county of Leicester. The Middle Lias consists of the following succession of beds arranged in descending order : — Thickness in feet. 5. The Rock-bed or Marlstone Rock 6 to 18 4. Sandy shales and light blue clays with bands of ironstone balls about 30 3. Blue clay, with flattish septarian concretions 20 to 30 2. Blue micaceous clays with septaria and many fossils. . . . ] I. Beds of soft ferruginous and micaceous sandstone alternating 1- 50 to 70 with light blue clays I The four lower groups form the zone of Ammonites margaritatus, which thus has a thickness of from 100 to 120 feet. The Marlstone Rock forms a separate zone, that of A. spinatus. The lower clays of the A. margaritatus zone are found only in the north-west corner of the county by Whissendine, Ashwell and Teigh ; they yield many fossils, of which the commonest are A. margaritatus^ Belemnites elongatus, Cardium truncatum, Modiola scalprum and Pkuromya costata. The higher beds are exposed in some brickyards near Oakham and Langham and also at Belton west of Uppingham, but fossils are rare in them. The Marlstone Rock is a ferruginous limestone, often passing into good workable ironstone. In its natural unweathered state it is a hard crystalline rock of a blue or green colour, but near the surface it is oxidized and weathered into a soft brown rubbly stone. It consists of several beds, some of which are harder than others, and they are usually crowded with fossils ; the shells of Rhynchonel/a tetrahedra and Terebratula punctata are especially abundant and often form calcareous masses or agglomerations, the interior of every shell being filled with crystalline calcspar. Other common fossils are Belemnites paxillosus, B. e/ongatus, Pecten cequivahis, P. dentatus, Hinnites abjectus and Avicula inaquivahis. This rock has been quarried both as a building-stone and as iron-ore. Its main outcrop enters the county about two miles south-west of Whis- sendine, passing first north-eastward and then southward into the vale of Catmose by Langham and Oakham to Egleton and Nether Hambleton. Inliers of it and of the underlying shales are found in the valley of the Gwash near Braunston, in the higher part of the valley of the Chater, and again round Belton, Wardley and Stockerston in that of the Eye brook ; this last tract is shown as part of the main outcrop on the old map (sheet 64), but a recent revision of this district by Mr. Fox- Strangways has led him to think that the outcrop of the Marlstone Rock is continuous beneath the drift from Tugby through Skeffington.' Where the Rock-bed forms the subsoil, as in the Vale of Catmos, the soil is of a bright red-brown colour, and being highly productive is almost everywhere ploughed and cropped, being thus in marked contrast to the adjacent slopes of Upper Lias clays which are usually left in the state of pasture land. 3
 * See 'Geology of the County near Leicester,' Mem. Geol. Survey, p. 36 (1903).