On two former occasions I have given some account of the deposit immediately underlying the London Clay, as well as of that which, to the eastward of London, lies upon the Chalk, and which I have respectively termed the “Basement Bed of the London Clay” and the “Thanet Sands†.” Between these divisions, which form the upper and lower portions of the Lower London Tertiaries, is a group of sands, pebble beds, and mottled clays, extending from Sandwich to Mariborough and from Newhaven to Dorchester. This group, with the two above-mentioned, completes the series of these Lower Tertiaries, and is the one which more particularly embraces the beds which have hitherto been described as the “Plastic Clay Formation,” exhibiting in one part of its range the mottled clays of Reading and Newbury, and, in another, the clays and sands, with fluviatile and æstuarine shells, of New Cross, Woolwich, and Bromley. Some of the principal sections in these localities have been described by Parkinson, Webster†, Dr. Buckland‡, Phillips and Conybeare§, Morris∥, Mitchell, Richardson††, Warburton‡‡, and more recently by the Rev. Mr. De la Condamine§§; whilst outlines of some underground sections have been planned by Mr. R. W. Mylne∥∥, and a short notice relating to the superposition of these and the other Tertiary strata has lately been given by M. Hébert***. But nevertheless the correlation of. the beds at the different sections has not, I conceive, been correctly shown, and the position which the strata of the Reculvers and Herne Bay hold with