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 A HISTORY OF NORFOLK Shouldham and South Runcton. A brickyard showed 15 feet of Kimeridge Clay, and a well proved the clay to be 50 feet thick and to rest on Lower Greensand. It may be observed that ordinary Chalk weathers at the surface into a kind of rubble. No doubt when the ice-sheet was forming over the district much of this rubbly Chalk was frozen to its base, and thus were incorporated in the Boulder Clay numerous pellets and tiny boulders of Chalk, which during the movement of the ice-sheet would become scored by pressure against tiny fragments of flint along the shearing planes of the ice. The Chalky Boulder Clay spreads in a tolerably connected mass over the low plateau of South-east Norfolk. In these tracts it is a much more tenacious clayey drift than it is in West Norfolk, where it is not only less continuous but is thinner and the soil is more marly and sandy, and forms large heaths and warrens.' There sand-storms occur after dry weather, when strong winds arise, and the soil is blown away from the surface. The heaths between Watton and East Harling which extend to the south-west from Croxton to near Thetford, form what is known as the ' Breck district.' Here the Chalk is thinly covered by Boulder Clay, and the whole has been sprinkled over with sand, for the most part wind-drifted. As Henry Stevenson remarked, the ' brecks ' include tracts which have been ' broken up ' by the plough at one time and after- wards abandoned as arable ground, but the district also includes extensive areas which have never been cultivated.^ The sand is derived partly from patches of drift sand found here and there on the Boulder Clay and Chalk, and partly from the decomposition of the sandy Boulder Clay. A remarkable sand-storm occurred in 1668 on the Suffolk borders, at a place called Santon Downham,' and much of the sand at that time spread into Norfolk. Wherever the Chalky Boulder Clay occurs there are found in almost every field evidences of old ' marl pits,' now usually ponds. In some of the large fields two or more of these excavations may be found. Some, like the Brooke meres, may have been excavated for other purposes as reservoirs of water for cattle, or even for the human population. The Boulder Clay itself weathers into a brown stony loam, and this decalcified Boulder Clay, which rests on a piped surface like that of the Chalk, is occasionally dug for brick-making, as at East Rudham and Harpley. It is con- spicuous again near Burlingham and Lingwood. A Roman kiln found at Kirby Cane, indicates the early working of one of the deposits. Apart from the surface brickearth the Boulder Clay has been largely used for the manufacture of ' clay-lumps,' rectangular blocks of clay, well worked up with chopped straw and made in moulds 1 8 inches long by 9 inches wide and 6 inches thick. Then dried in the sun the clay-lumps ' See F. J. Bennett, ' Geology of Diss,' {Geol. Survey), p. 14. ' Stevenson, Birds ojf Norfolk, vol. i. p. li. ' F. J. Bennett, 'Geology of Attleborough,' etc. {Geo/. Survey), 1884, p. 1$; and ' Geology of Diss,' etc. {Geo/. Survey), 1884, p. 5. 20