On the Investigation of the Mechanical Constitution of Loose Arenaceous Sediments by the method of Elutriation, with special reference to the Thanet Beds of the Southern Side of the London Basin

Abstract

The mechanical constitution of a detrital sedimentary deposit is the aggregate result of the operation of a complex suite of physical laws which govern transport of detrital material by, and its deposition from, water in motion. These physical laws have been elaborately investigated by many workers, and while much remains obscure, important conclusions have been achieved. The detailed examination of the mechanical constitution of the sediments of the geological column has been neglected, although a few pioneer workers have obtained notable results. Sediments of economic value have received attention, but in the realm of pure geology workers have been slow to take up the investigation. Accumulating results indicate, however, that geologists would do well to devote attention to this line of research. Distinctive results are being obtained from sediments, which, even though they may not lend themselves at the present time to complete interpretation, from the point of view of reconstruction of the conditions under which the said deposits were formed, nevertheless bid fair to provide the geologist with another weapon in his armoury. Fluviatile deposits have been found to possess a mechanical constitution distinct from that of estuarine sediments, and the latter are again clearly differentiated, mechanically, from purely marine formations. It may be remarked, too, that the nomenclature in current use applied to the loose sedimentary deposits lacks that element of scientific precision so desirable and necessary if proper progress is to be made. Such terms as “sand”, “clayey sand”, “sandy clay”, and “clay” are at present employed by different writers in different senses, and some system of classification which would give definiteness to the meaning of these and similar terms appears to be urgently called for. The only satisfactory basis for such a classification must be a quantitative one, depending upon mechanical analyses of sediments. When a sufficiently comprehensive collection of comparative data is available it should be a simple matter to devise an adequate scheme for the classification of the loose detrital sediments.