18 Tlir BlacJxicater Valley, Essex. 



accumulated waters. The gravel brought down into this 

 lake by the Guith and Blackwater forms a continuous terrace 

 from Witham to Brain tree, interbedded with shell-marl, 

 swamp-mud, and brick-earth, as described in the Geological 

 Survey Memoir on Sheet 47.^ The elevation continued till 

 the dee^) channels of the Essex estuaries were formed, when 

 subsidence took place, readmitting the sea as far as Col- 

 chester, Maldon, and Battle Bridge. I have elsewhere pub- 

 lished reasons for believing that a slight subsidence is now 

 in progress.^ 



Those who care to investigate the origin of the undulation 

 described above may be interested in hearing that a parallel 

 undulation has been noticed in the Chalk ridge above 

 Eoyston, with an outward north-westerly dip of 60^, and 

 that the prolongation of the line of Tiptree Heath coincides, 

 near Deptford, with a fault bringing up the Chalk through 

 the Tertiaries, and, in the opposite direction, we have Chalk 

 coming to the surface in an abnormal way, at Shelly (near 

 Hadleigh) and at Ipswich, whilst farther away in Suffolk 

 other points of disturbance have been noticed along a line 

 nearly coincident with the Yarmouth branch of the Great 

 Eastern Eailway. 



I must defer to another occasion my reasons for suj)posing 

 that the undulations are confined to the upper 1000 feet of 

 the earth's surface, and are due to lateral pressure in the 

 Chalk, and that the subjacent Coal-Measures or other rocks 

 are not affected thereby. 



Wliitaker, W., W. H. Penning, W. H. Dalton, and F. J. Bennett. 

 'The Geology of the N.W. Part of Essex and the N.E. Part of Herts., 

 with Parts of Cambridgesliire and Suffolk.' — Geological Survey Memoir. 

 8vo. London. Pp. vi., 92 ; 19 woodcuts. Price 3s. 6 f/. 



2 ' Subsidence in East Essex.' — Geol. Mag., dec. ii., vol. iii., pp. 491 — 

 493. (1876). 



