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 A HISTORY OF SUFFOLK a few places, as near Brandon, hard beds have been employed for build- ing purposes. The most interesting industry connected with the Chalk has been that of the manufacture of gun-flints in the neighbourhood of Brandon. The flint was largely obtained from Lingheath, a tract described by Mr. S. B. J. Skertchly ' as completely honeycombed with pits, many of them old, and most of them approached through shafts about 45 feet deep. These occur from Brandon Park on the west to Santon Down- ham Warren on the east. Good flint has also been obtained at Elvedon, and at one time it was largely extracted from pits on Icklingham Heath. According to the same author the best bed of flint is the ' Floor Stone,' which is the band to which the pits are sunk, and from which most of the gun-flints have been made. It is generally a continuous layer, smooth at the base, and with a somewhat irregular surface. Other layers have been occasionally used for gun-flints, but have been more extensively employed for building purposes, a trade still carried on. About the year 1835, when percussion caps were introduced, the gun- flint manufactory rapidly declined, the materials subsequently shaped being chiefly for export to Africa. Dressed flints have been much used in building churches, and fine examples may be seen at Southwold and elsewhere. Flint boulders from gravels have also been largely used for building purposes. The Chalk is a deep-sea formation made up of calcareous ooze derived from the accumulation and decay of various organisms, notably foraminifera, as well as mollusca and echinoderms. Together with these were sponges, whose siliceous structures have furnished the material which has segregated into the irregular nodules known as flints. These nodules follow the planes of bedding. Other forms of flint occur as tabular layers and as vertical or oblique veins, and these have probably been formed by subsequent infiltration of waters which held silica in solution and deposited it along the more or less vertical and horizontal joint-planes. That the Chalk extended over the greater part of England is gener- ally admitted, so that on the partial upheaval of the area in Tertiary times Chalk cliffs alone yielded material in its flints for the formation of pebble beds. In Suffolk the Eocene strata do not yield any con- spicuous flint pebble beds such as we find in Hertfordshire and other southern counties, but in Pliocene and later times there were great accumulations of flint gravel which tell of the destruction of Chalk — a loss that is likewise manifest from the irregular extension of Pliocene and Glacial drifts across the eroded surface of the Chalk. This great plain of denudation is by no means a uniformly level tract ; it was worn down during successive stages of the Eocene period by encroachment of the sea westwards and northwards, and modified in various ways by the marine, fluviatile and glacial agents of subsequent ages, to which attention will be directed. ' 'Manufacture of Gun-Flints,' Geol. Survey (1879). 8