GEOLOGISTS used to ask themselves a riddle: How did the rounded outlines of the chalk denes and downs come to show the forms characteristic of sculpture by streams, since water runs straight through the chalk and does not form streams upon it? The acceptable answer to the riddle used to be that long ago the chalk below the surface was made impermeable summer and winter by frost, and that in the spring the snows of winter rushed off the frozen surface in torrents. Weather conditions last winter in our part of Wiltshire illustrated this strikingly in a way which the oldest inhabitant does not remember to have seen before. My house is in a dene in the chalk sloping gently to the Kennet for nearly two miles, with downs on each side. It will be remembered that there was first sharp frost with heavy snow-falls, then a few days thaw, and then again sharp and prolonged frost. The effect of this, no doubt, was to seal the chalk with a layer of absorbed and frozen water. During the second and prolonged frost there was the now celebrated incessant deposition of dew in the form of ice, and of snow, making a big accumulation of water on the top of the frozen layer. Then came the final thaw. With it, for the first time within living memory, a stream appeared and flowed briskly down the dene, doing a little water sculpture on its way and leaving some tiny deposits which will make good Combe rock in the future.
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Soil Use and Management (1993)