On the Origin of Dry Chalk Valleys and of Coombe Rock

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Abstract
For many years the singular mass of angular flints and Chalk, known as the Brighton Elephant-bed, has been familiar to geologists. This deposit I had not seen till 1884, when I was instructed to examine, for the Geological Survey, the Pleistocene deposits of Sussex between the escarpment of the South Downs and the sea. Coming from eight years' work in strongly glaciated districts, I was at once struck by the appearance of the Elephant-bed—or, as it is called in the district, the “Coombe Rock.” It is a very different deposit from anything commonly seen in the Yorkshire or Lincolnshire Wolds, and different, though not so markedly different, from anything found in Norfolk. This occurrence in a non-glaciated district of a type of gravel unlike anything of ordinary occurrence in glaciated districts of similar configuration aroused my interest. After two years' study of the beds in the field, I venture to bring forward my views as to the mode of formation of Coombe Rock and as to the origin of dry Chalk Valleys—two subjects intimately connected. The configuration of the surface beneath the drift on the seaward side of the South Downs is identical with that found in the Chalk districts of Yorkshire and Lincolnshire. In each of these districts we have a dip-slope from the edge of the escarpment seaward. But this slope does not pass under the low-lying drift areas; it ends abruptly in a cliff, now much degraded, but still recognizable as a sea-cliff both by the marine

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