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A. Horton (Institute of Geological Sciences)
The nature of the drift in the Fenland river basins reflects repeated variations from cold to temperate climate conditions. Fall in sea level during the glacial periods resulted in overdeepening of river valleys. Outlets of valleys 30 to 60 m deeper than at present were blocked by the Chalky Boulder Clay ice-sheet, and lacustrine sediments were laid down in finger lakes. These deposits vary from thinly laminated varved sediments through alternating beds of sand, silt and clay to beds of unsorted sediment of boulder clay type. In addition to these types of deposits, boulder clays of Chalky Boulder Clay lithology are the most extensive deposits in the Fenland basin glacial sequence.
Modern rivers may have in part reexcavated their original valleys, but some blocked pre-glacial valleys occupy interfluves of modern rivers. Pleistocene terrace gravels occur in all Fenland valleys.
Genetic influences on the engineering properties of tills
A. McGown (Dept. of Civil Engineering, University of Strathclyde) and E. Derbyshire (Dept. of Geography, University of Keele).
Tills, while collectively distinguishable from other engineering soils, are inherently very variable, and individual till deposits can behave quite distinctively. This can be related to the somewhat differing geological histories of the deposits and to variations in many other, often derived, properties of tills. It is thus submitted that establishing the geological history of any till will, when its modes of formation, transportation, deposition and post-depositional processing are all considered, produce
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