GEOLOGY 



cliffs at Clacton, and many were formerly dredged to the south of 

 Harwich for the manufacture of Roman cement. The cracks or septa 

 arc filled with calc-spar, and sometimes contain pyrites or ' copperas.' ' 

 The septaria no doubt originated from the segregation of the more 

 calcareous portions of the clayey mud after the deposition of the London 

 Clay. Morant says these nodules were used in the walls of Colchester. 



The London Clay has been extensively dug for brick-making and 

 especially for tile-making, as at Buckhurst Hill, Loughton and elsewhere. 

 The loamy beds which occur at the junction with the Bagshot Beds, as 

 at Brentwood, near Theydon Bois and on Epping Plain, are very suitable 

 for brick-making. 



The soil is naturally thin and tenacious, and has been described as a 

 cold, heavy and wet clay on tile-earth ; but it is ameliorated on the 

 slopes where the higher grounds are covered by Bagshot Sands or drift 

 gravels. On the stifFer grounds of Epping Forest the oak and hornbeam 

 find a congenial soil. 



BAGSHOT BEDS 



Overlying the London Clay, and connected with it by alternations 

 of sand, loam and clay, are the Bagshot Beds. These consist in mass 

 of fine buff-coloured sand with thin layers of pipeclay, overlaid in 

 places by pebble-beds which are mainly composed of flint pebbles. The 

 occurrence of zircon among the minute materials of the Bagshot Sands 

 at High Beech was detected by Mr. A. B. Dick.* The formation occurs 

 in outliers, which are but remnants of a wide-spread deposit. These 

 outliers constitute some of the higher and more picturesque tracts, as 

 at Epping and High Beech (362 feet), Brentwood, Warley (360 feet), 

 Billericay, Stock, Langdon Hill (385 feet), Rayleigh and a few other 

 localities. The land is less cultivated than on other formations, and 

 commons, village greens and much woodland help to diversify the scenes. 



From the fact of this gradual passage from the London Clay into 

 the Bagshot Beds there has arisen considerable difference of opinion with 

 regard to the boundary line that should be drawn on geological maps to 

 separate the two formations. Those who, like S. V. Wood, jun., take 

 the first prominent bed of sand in the ascending series to indicate the 

 Bagshot Beds, would mark much larger areas of that formation, notably 

 along the high grounds from High Beech to Epping, and between 

 Theydon Mount and Northweald Basset. On the other hand those who 

 in the downward succession take the first mass of clay to belong to 

 the London Clay indicate much smaller areas of Bagshot Beds. In the 

 one case we have to map clay in the Bagshot Sand, and in the other sand 

 in the London Clay. Absolute consistency is not however to be obtained, 

 and the difficulties met with in deciding about a boundary near Epping 

 are encountered also near Brentwood and Rayleigh. 



Some casts of shells, apparently Turritella, Natica and Valuta were 



1 Hence perhaps the name Copperas Bay, west of Harwich. Copperas (sulphate of iron) is manu- 

 factured from pyrites. See also P. Morant, Hilt, and Antiq. f Etiex (1768), vol. i. p. 500. 



1 Whitaker, Geology of London, vol. i. p. 523. 

 I 9 2 



