Page:VCH Northamptonshire 1.djvu/66

 A HISTORY OF NORTHAMPTONSHIRE The most extensive fault, longitudinally, is perhaps the Great Nene Fault, which appears to follow the river's course for some 1 1 miles, that is from west of Weedon to east of Northampton. At Northamp- ton the dislocation, or throw as it is called, is about 70 feet, the northern side being the lower. This fault has had an important beneficial influence on the deep-seated water-supply of the town. Both folds and faults are important when considering the possible water-supply of places. Scenery as Dependent on Rock Structure The various denuding agents which, acting on rocks of unequal hardness and different chemical constitution, produced hills and valleys, left exposed to the atmosphere characteristic land surfaces, on which soils were gradually formed varying in composition and suitability for different forms of plant life. The soils will be treated of elsewhere in this book, but of the land surfaces a few remarks may here be made. The thicker clay beds of the Lower and Upper Lias and Oxford Clay, when not capped by other formations, present very similar features — a gently undulating country, or regular and well-rounded hills. The Middle Lias, owing to alternations of hard and soft beds in it, and particularly the thick rock-bed at its top, forms rather flat lands, but the sandy micaceous clays between the hard beds, having a higher co- efficient of friction than any other clays of the district, form steeper slopes into intersecting valleys. The Northampton Sand in the western and northern parts of the county mostly forms a cap to the hills, and where it does so the hill has a flatter top than clay alone would assume. On the scarp-slope of such a hill the junction of the Northampton Sand with the Upper Lias Clay below can generally be detected at a distance by a pretty sudden increase of slope, from 1 0° or 1 2° to 1 5° has been observed at several places about Preston Capes, Everdon, etc. Where the formation occupies an extended area, rather flat land results, because the rainfall sinks in instead of running over the surface. The limestones of the Lincolnshire Oolite, Great Oolite, and Corn- brash, where fairly thick, form on the whole wide-spreading plains, or flat lands not much divided into hills and valleys. The thin beds of the Great Oolite Clay, and the Upper and Lower Estuarine series have no extended influence on the scenery, but on a slope may produce a step-like arrangement by giving a steep dip between harder beds, the Cornbrash and Great Oolite for instance. Fenland The district of the Fens deserves special notice for several reasons. Owing to the fact that Northamptonshire does not reach the sea, there is a comparatively small amount of fenland within its borders, some 10,000 acres only, embracing Peterborough Flag-Fen, Newborough Fen, and Borough Fen. The land is mostly below high-water mark, and would be covered by the sea at high spring-tides but for the various 34