On the relation of the Westleton Beds, or pebbly sands of Suffolk, to those of Norfolk, and on their extension inland : with some observations on the period of the final elevation and denudation of the Weald and of the Thames Valley, etc. / by Joseph Prestwich.

  • Prestwich, Joseph, 1812-1896.
Date:
1890
Catalogue details

Licence: Public Domain Mark

Credit: On the relation of the Westleton Beds, or pebbly sands of Suffolk, to those of Norfolk, and on their extension inland : with some observations on the period of the final elevation and denudation of the Weald and of the Thames Valley, etc. / 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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    •JT the old designatious of “Plastic Clay ’’and “ Mottled Clays,” which would specialize characters common in formations of Tertiary as well as of Secondary age. Tho localities where the Shingle Beds are most extensively de- veloped, and where the joint lithological and palajontological cha- racters are best combined, wUl be found in the Ordnance Map, Sheet 49 W. and 50 E. From this centre I will first take their range northward. Between estleton and Dunwich there is a largo tract of common, formed by low hills of pebbly shingle, which extends with little interruption to Blythburg and Southwold, and thence to Easton Bavant and Covehithe, forming a belt some 2-4 miles wide and 10 miles long. The higher ground is everywhere capped by Boulder- clay, from beneath which the Shingle Beds crop out, whilst on the coast the Chillesford Clay rises from beneath the latter fexcept where it has been denuded before the deposition of the Shingle), thus defining accurately the stratigraphical position of the Shingle Beds. The Shingle consists of flint pebbles as well rounded and forming beds as massive as the Tertiary Beds of Blackheath or Addington, with subordinate sands and thin clays. From two of the closely adjacent large pits on the common, the accompanying general section (fig. 1) is constructed from notes taken some years since. Unlike the overlying Glacial Beds with their northern drift, we have evidence in this Shingle of a decided tran.sport from the south- ward in the presence of subangular worn fragments of Chert and llagstono of the lower Greensand, probably of Kent, a fact to which I formerly drew attention *. With these are associated a considenible proportion of small white quartz-pebbles and a few large flattish ovoid pebbles t of light-coloured Quartzite and Sand- stone, with small pebbles of Lydian stono and jasper &c. There is a total absence of the larger darker red and grey rounded quartzite-pebbles (cobbles) of the New Bed Sandstone, so common in the Glacial Scries. Tlie average composition i of this Westleton Shingle at Westleton may be roughly taken as under:— Per cent. 1. Blnck flint-pebble* 60 2. While quartz-pebbles, with a few rose-coloured 20 8. Subangular flints, not stained 10 4. Subangular fragments of grey pin-hole ragstone and dark yellow chert 4 5. Large flattish pebbles of light-coloured quartzite, light and dark sandstones, and small pebbles of veinstone, Lydian stone, and jasper, with a few subangular fragments of black chert (Carbo- niferous ?), of a dark slaty rock, and of quartz 6 100 ♦ Op.eiV. pp. 461 and 477 (1871) ; and British Association Reports for 1881, p. 620. t Thev are very similar in shape and colour to the recent quartzite-pebbles on the Chesil Bank. ■ i ts J The determinations in all cases can only be given approximately. For reasons given in Part II. of this paper these proportions may not be quite correct locally ; but as the same error, if any, runs through all the localities, the general result is not seriously affected.