The Clay-with-flints has a patchy, but extensive, outcrop in southern England south of the limit of the Anglian ice sheets, and in\ud northern France where it is referred to as the Argiles à silex. Since early Victorian times, when it was recognised that its principal\ud components were clay and unworn flints, the deposit has been presumed to have been derived from the dissolution of large\ud volumes of chalk. It was also recognised, however, that the clay contents of typical chalks were too low to have produced the\ud clay-flint ratios of much of the Clay-with-flints. The additional clay, together with sand that could not have been derived from\ud the Chalk Group, was therefore presumed to be of later origin. The solution hypothesis remained largely undisputed until the\ud 20th Century, even though there is no published example of an intermediate stage in the process in the form of a layer of partially\ud dissolved chalk. The age of formation of the Clay-with-flints has long been the subject of dispute, partly because of the absence\ud of palaeontological evidence, and partly because the name has been applied to a wide variety of lithologies including reworked\ud and remobilised materials. Suggested ages range from Palaeocene in parts of northern France to Pleistocene in the London Basin.\ud In east Devon and west Dorset, beds of partially dissolved in situ Upper Greensand and Chalk tens of metres thick are overlain\ud by Clay-with-flints. They confirm the importance of large-scale solution as a contributing factor in the formation of the deposit in\ud south-west England. The partially dissolved layers and the Clay-with-flints were folded and faulted in the Miocene, and they can\ud be seen to pre-date Pleistocene erosional features including hanging dry valleys and frost-wedge pipes. The principal phase of\ud dissolution is presumed to have been in warm moist climates during the Palaeocene-Eocene Thermal Maximum
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