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 GEOLOGY the strata a process which continued into the Pliocene period, when the north-eastern portions of the area were submerged and received banks of the shelly sand known as Red Crag. How far this Pliocene submer- gence extended it is difficult to say, for although there are some high-level or plateau deposits of pebble-gravel which may date back to Pliocene times, there is no evidence from fossils to prove the point 1 (see p. 12). Prior to the Glacial period the more prominent physical features of the country had been formed, as the Bagshot Beds must have been largely removed, only scattered outliers remaining on an irregular found- ation of London Clay ; and Mr. T. V. Holmes has pointed out that as a thickness of 400 feet of London Clay (nearly the full thickness) has been proved at Dagenham, it is probable that some outliers of Bagshot Beds may have diversified the surface in that neighbourhood just prior to the formation of the Thames valley. 4 RED CRAG The Red Crag is one of the more attractive of geological formations, mainly because fossils are readily to be obtained and partly because the exposures occur for the most part in pleasant places. In Essex the most famous locality is Walton-on-the-Naze. As early as 1703 the fossils of Harwich cliff were noticed by S. Dale,* and they were more prominently brought before the public in the descriptions and figures published in his appendix to Silas Taylor's History and Antiquities of Harwich and Dovercourt* From this account we learn of an outlier of the shelly Crag that has since been destroyed by the ravages of the sea. Attention was drawn to another outlier at Beaumont, by John Brown of Stanway, while small tracts occur between Harwich and Little Oakley, at Mistley, and again in the country from Langham to near Boxted. Some of these remnants of the Crag have been noticed at the surface, others have been detected from the material brought up in occasional borings or well-sinkings. A phosphatic nodule-bed at the base of the Crag was at one time worked at Wrabness and also at Walton-on-the-Naze. The Red Crag in Essex is regarded as the oldest portion of the formation, and from its development at Walton-on-the-Naze, it has been termed the Waltonian stage by Mr. F. W. Harmer. 6 He observes that the majority of the characteristic shells found in it are either extinct or south-European forms : they include Cyprcea ave/fana, Voluta lamberti, Purpura tetragona, Trophon (Neptunea) contrarius, and many others. A band of clay above the shelly Crag at Walton has been regarded as a representative of the Chillesford Clay of Suffolk, but this correlation is questioned by Mr. Harmer. 1 See Whitaker, Geology of London, vol. i. pp. 290, 494. * Eitex Nat., vol. vi. p. 145. Phil. Trans., vol. xxiv. (1704) p. 1568, in a letter to Edward Lhwyd, 1703. 1730, ed. 2, 1732. Geol. Survey, 1890. II
 * Quart. Journ. Geol. Sot., vol. Ivi. p. 709 ; see also C. Reid, ' Pliocene Depotiu of Britain, Mtm.