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 GEOLOGY Essex possesses one mineral water which attained a temporary reputation. This was at Hockley Spa, where a permanent spring issues from the base of the Bagshot Sand. Here about sixty years ago an endeavour was made ' to establish a Spa with pump-rooms, and a woman was employed to dispense them, whose strong healthy appearance visitors were led to believe was the result of the medicinal effects of the water,' but ' the speculation proved a failure.' 1 Dr. A. B. Granville, writing in 1841, gives an account of the discovery of the mineral water, and states that it contained sulphates of magnesia and lime, carbonate of lime, and chloride of sodium. 1 With the growth of population the supplies of water from shallow sources have in many cases become not only inadequate, but also con- taminated ; and even when the supply remains sufficient for a small country village the danger from pollution is great, especially if any serious illness arises. The whole aspect of Essex appears geologically to be one of some- what sluggish repose despite the constant waste of the ground by rain and rivers and sea. The force of the breakers is however broken by the shallow ground which borders a great part of Essex. Nevertheless geological action occasionally makes itself manifest in a more startling manner. In 1884 a remarkable earthquake was felt especially in the country between Colchester and the mouth of the Blackwater ; and according to the detailed investigations made by Prof. R. Meldola and Mr. W. White it was ' the most serious that has happened in the British Islands for about four centuries.' They state that the number of buildings damaged by the shock was between 1,200 and 1,300, including 20 churches and 11 chapels, and that the main axis of damage had a general direction from north-east to south- west, extending from Wivenhoe to Peldon. The effects produced may, in their opinion, have resulted from the rupture of deep-seated rocks under strain or pressure, such as the sudden production or extension of a line of faulting ; and the localization of the damage was probably due to the disturbance having originated under a clay area. 3 i H. W. Bristow in Whitaker's Geo/egy of London, vol. i. p. 26 1. 'Report on the East-Anglian Earthquake of April zznd, 1884,' Essex Field Club Special Memoirs, vol. i. (London, 1885).
 * The Sfai of England, vol. iii. p. 606.