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. 



* Quart. Journ. Geol. Sot., vol. Ivi. p. 709 ; see also C. Reid, ' Pliocene Depotiu of Britain, Mtm. 

 Geol. Survey, 1890. 



II 



