On the age, formation, and successive drift-stages of the valley of the Darent : with remarks on the Palaeolithic implements of the district, and on the origin of its chalk escarpment / by Joseph Prestwich.

  • Joseph Prestwich
Date:
1891
Catalogue details

Licence: Public Domain Mark

Credit: On the age, formation, and successive drift-stages of the valley of the Darent : with remarks on the Palaeolithic implements of the district, and on the origin of its chalk escarpment / by Joseph Prestwich. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    ])ebbles derived evidently from the lied Clay-witli-flints, and from the Lower-Eocene strata on the adjacent hills. This red argillaceous rubble is certainly not rainwash, nor can it be the result of surface disintegration. At present, however, I am only concerned with the fact of its being a drift or covering which precludes us from assigning the Chalk-rubble which underlies it to such existing causes as rainwash or weathering. Not being worked for any purpose, it is rarely that sections of these “ rubbles ” are to be seen. Of the few that have come under my notice in this valley, the following (fig. 12) is an example. It occurred in digging a pit about 10 to 12 feet deep for a reservoir in a field on the slope above Sepham Earm, near Otford. Eig. 12.—Section on Sejoham Farm, on the loiuer slope of the Chalk hills. Red ai’gillaceous rubble with dispersed Cbalk flints and Tertiary pebbles. 2'. Cbalk-rubble of broken chalk and sharp angular flint-fragments in a chalk-paste, passing into— 2. Solid Chalk with layers of flint. The two beds (a’ and 2') are perfectly distinct, and never pass one into the other ; 2', on the other hand, does not form a sharp line with the underlying Chalk, but graduates into it. The height of the ground is about 280 feet above O.D., and 90 feet above the level of the Darent. The Red rubble is easily recognized in the ploughed fields by its colour. But while this is local and only covers certain areas in the valleys intersecting the Bed Clay-with- flints plateau, the white “ Chalk- and flint-rubble ” is more general *, passing under the Bed rubble, as well as over the wider intervening spaces. In those valleys to which it is limited it rises to a considerable height on the slopes and descends to the bottom of the valley. Erom the position and character of the White rubble, in which the Chalk forms a pulverized paste with dispersed subangular frag- ments of chalk, sharply angular flints—broken but otherwise un- altered—and occasionally some Tertiary flint-pebbles, and a few fragments of ironstone and chert from the Lower Greensand, it is, I think, not improbably Glacial waste connected with that stage of valley-erosion which preceded the drift f, and of which the festoon- ing of the Chalk is a subordinate feature. Just east of Otford, at the angle formed at the junction of the Holmesdale Valley with the pass of the Darent Valley through the * ‘Chalk- and flint-rubble’ was said to underlie the Mammoth-gravel at Shoreham.