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 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