Page:VCH Rutland 1.djvu/40

 A HISTORY OF RUTLAND had previously been the floor of a clear open sea in which even corals could exist, was suddenly converted into an estuary or a bay of shallow water which was constantly turbid with the mud and silt carried into it by one or more rivers. The beds above the ironstone band consist of variously coloured clays — blue, black, green, grey and white — with occasional courses of sandy limestone and layers of fibrous carbonate of lime called 'beef by the quarrymen. In some of these beds the fossils are marine, including shells of Ostrea, Modiola, Card'mm and Cuspidaria ; in others they belong to freshwater genera such as Uw/o, Cyrena and Paludina ; while the black carbonaceous clays generally contain plant remains and pieces of wood. The usual thickness of this set of beds is from 20 to 30 feet. (2) Great Oolite Limestone. — This division consists of alternat- ing beds of whitish limestone and marly clay with occasional layers made up of small oysters (0. Soweriyi a.nd 0. subrugulosd). The limestones are usually soft, white and marly, but are sometimes more or less shelly. They are seldom oolitic, and thus differ from those of the Lincolnshire Limestone. When protected by any thickness of clay the beds are bluish and hard. There is always a complete passage downward into the Estuarine clays and upwards into the Great Oolite clays. Many of the fossils which occur in these beds range up into the Cornbrash, but there are a few which by their special abundance serve to charac- terize the Great Oolite ; these are the oysters above mentioned, with Modiola imbricata, Homomya gibbosa, and Clypeus Mulleri. In some places too the palatal teeth of a kind of shark [Strophodus) are not uncommon and are called fossil slugs by the workmen. Corals are sometimes found, a species belonging to the genus Isastrea being abundant near Essendine. The Great Oolite Limestone caps the slopes and spurs of the Upper Estuarine clays, forming flat-topped tabular hills, which give a distinct character to the scenery of the district in which they occur. The soils of these beds are of high value to the farmer in consequence of the mixture of calcareous and argillaceous matter which they contain ; being heavier and more retentive than that of the Lincolnshire Lime- stone they are more favourable in seasons of drought. (3) Great Oolite Clay. — This was called the BHsworth Clay by Mr. S. Sharp,' but the name has not yet been generally adopted. Its component beds are of various colours — blue, purple, green and yellow, with occasional layers of calcareous or ferruginous nodules. Fossils are not common in this part of the series, but there are some- times thin seams made up of a small oyster-like shell {Placunopsis socialis), and bones of the large dinosaurian reptile called Cetiosaurus have been found at Banthorpe and Essendine north-east of Stamford. These clays vary in thickness from i 5 to 30 feet, but they seldom form a band of any width, only a steep slope between the two plateaus • See ^art. Joum. Geo/. Soc. xxvi, 380. 8