GEOLOGY brackish water forms ; plant beds occur, from which it would appear that a kind of equisetum covered a great many square miles of the swampy ground ; and false-bedded and ripple-marked sandstones indicate shallow water. It is probable that the river or rivers came from the north- west.' The Lincolnshire Oolite The latter part of the Inferior Oolitic period in this district was characterized by a local depression over an area of some ninety square miles, embracing chiefly north-east Northamptonshire and Lincolnshire. The extreme westerly (Maidwell) and southerly (Wold) limits of the Lincoln- shire limestone now to be seen are probably not far from the boundary of the original depression in these directions. The main mass of the Lincolnshire Oolite consists of compact, subcrystalline, oolitic, fossiliferous, and slightly argillaceous limestones ; and of shelly ragstones (Barnack Rag, etc.), towards the formation of which coral contributed much. The beds thicken in a north-easterly direction to about 75 feet at Stamford, in which direction no doubt the deeper water lay. Nearness to land and shallow water is indicated by wood, plants, and rolled shells, indeed the limestone appears to have been in places a dead-shell bank. The lower beds may be marly and soft, but a good portion of the stone furnishes a cream-coloured freestone suitable for ornamental work, as well as general building purposes. A hard shelly variety takes a good polish, and is known as Weldon marble, Stamford marble, etc., according to the place from which it comes. All forms produce lime of good quality. Collyweston Slates. The lower beds of the Lincolnshire Oolite formation in those parts that may be looked upon as the margin of the depression in its earlier stages, are either sands or sandy limestones or both. The arenaceous limestones have been largely worked at Dene, and between Stamford and Collyweston and elsewhere, under the name of Collyweston Slates. At Collyweston the workable bed varies from 6 inches to 3 feet in thickness, but more or less slaty beds occasionally encroach on the main mass of limestone to the thickness of 18 feet. Ripple marks, worm tracks, and plant remains in the slates, as also the sands, indicate shallow water and nearness of land." ' John W. Judd, ' The Geology of Rutland,' etc., Memoin of the Geological Survt't P- 129- ^ For more detailed description of these and other beds of the Inferior Oolite consult Sharp and Judd. John W. Judd, 'The Geology of Rutland,' etc., Mnnoirs of the Geological Survey ; Samuel Sharp, ' The Oolites of Northamptonshire,' pt. i., Quart. Journ. Geol. Soc. (Aug. 1870), p. 354 ; pt. 2, ihid. (1873), P- 225. 17
