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 A HISTORY OF LEICESTERSHIRE high ground about Waltham and Croxton Kerrial. The larger part of the area, however, does not rise much above an average of from 300 to 500 ft.; but, nevertheless, forms the watersheds between the tributaries of the Trent flowing north, those of the Avon flowing south-west, and those of the Welland flowing to the east. Five main groups of rocks are represented in Leicestershire : (i) the Pre-Cambrian rocks of Charnwood Forest ; (2) the Coal Measures of the Leicestershire and South Derbyshire Coalfield ; (3) the Red rocks, the Permian and Trias, lapping round them and covering a large part of the plain ; (4) the Jurassic rocks, comprising the three divisions of the Lias, and the few small patches of Oolite capping the eastern hills ; and (5) the superficial clays and gravels that overlie the other formation indiscriminately. The following are the subdivisions of the rocks that are exposed at the surface : Period Formation Character of the Strata Approximate Thickness in feet Recent. . . Pleistocene. Alluvium Jurassic. . River terraces Boulder-clay, sand and gravel. Inferior f Lincolnshire Limestone Oolite Northampton Sand 'Upper Middle Lower Triassic. . Permian. Carboniferous. Pre-Cambrian or Archaean Rhaetic Keuper Bunter Marl. Sandstone. Permian (?). Coal measures Millstone Grit. . . Carboniferous Limestone Charnian Silt, clay, peat and gravel. Gravel and loam Stony clay, sand and gravel Limestone and freestone Sands with layers of clay in the upper part, Ironstone below Clay and shale with calcareous concretions Ferruginous limestone and iron- stone. Sandy shales in lower part Clay and shale ; argillaceous lime- stone Black shale ; sandstone .... Red and variegated marl with bands of gypsum and a little sandstone Red sandstones with marl bands. Beds of shingle with a little sand- stone Breccia and red marl .... Shales with seams of coal and fireclay with beds of sandstone and ironstone Massive sandstones and coarse grits with beds of shale .... Limestone with occasional beds of chert Slates, hornstones and agglomerates with intrusive igneous rocks Up to 25 I Up to 150 Sc Up to 40 1 10 to 180 100 to 200 750 38 600 IOO o to 800 o to 50 500 or more zo to 500 Unknown The geology of Leicestershire has been previously treated by many writers, but only passing reference to the more general of these publications in these pages. 1 It is not, however, until late years that the '^ ' 2