A HISTORY OF ESSEX to the notice of Mr. T. V. Holmes through subsidences having occurred on account of the old workings. In these cases the Chalk was reached at a depth of about 12 feet, 1 and was probably dug for agricultural purposes. The Chalk itself has little direct influence on the agriculture, but open down-like tracts occur near Saffron Walden, and the soil generally on the uplands bordering the Cam valley and extending to Heydon is dry and more or less ' hurrocky,' that is mixed chalky and gravelly. 2 Along the Cam valley below Newport many springs issue and there are good watercress beds. In very wet weather the valley is liable to be flooded from the drainage off the clay uplands. During excavations at Grays a former proprietor, Richard Meeson, opened up some copious springs which were afterwards utilized for the water supply of a considerable district. 3 The Chalk indeed is of the greatest importance as a water-bearing formation, and from it supplies are obtained in many a well in Essex. The rain falling on the North Downs and on the downs in Hertfordshire and Cambridgeshire descends into the trough of Chalk which underlies Essex. Here the water is pent up beneath the mass of Tertiary strata, chiefly London Clay, and borings carried into the Chalk yield a varying supply. There is no doubt that the Chalk below sea-level is saturated, and this plane of saturation rises inland to some extent with the rise of the land and the amount of rainfall ; but when covered by a great thickness of Tertiary strata the Chalk itself is firmer and closer than it is near the surface. There are fewer fissures, and therefore a free supply at a great depth is not to be depended upon. Water may be pumped faster than it can be replaced. Saturated Chalk of course acts like an im- pervious stratum, and the additions flow away in springs. Thus overflows from this Basin escape at the surface on the margin of the Tertiary strata, as at Benfield Springs near Bishops Stortford on the north, and at Grays and Purfleet on the south. On the far northern side of the Chalk Basin there is a copious outflow beyond Heydon along the outcrop of the Totternhoe Stone, and numerous springs issue at and below Newport in the Cam valley. Pumping from deep wells takes so much from the body of the Chalk, and the amount is naturally lost to the springs. THANET BEDS Overlying the Chalk there is generally to be found a mass of pale and greenish-grey sand and sandy clay. This formation known as the Thanet Beds contains at its base a layer of green-coated flints, which appear to have originated from the dissolution of the upper layers of Chalk in which the flints were formerly embedded. The strata are exposed between Purfleet and Aveley, at StifFord, 1 Essex Nat., vol. iii. p. 183. 8 C. Vancouver, General View of the Agriculture of Essex (1795) pp. 104, 105. 3 Prestwich, Quart. Jount. Geol. Sac., vol. xxviii. p. xliii. ; see also Minutes of Evidence, Roy. Comm. on Metrop. Water Supply, 1893. 6
