A HISTORY OF SUFFOLK gravel and buff sand, hardened in places into stone, which may belong to the Oldhaven or Blackheath Beds. Again, beneath the London Clay at Leiston, a boring proved 26 feet of loamy sand with flint peb- bles and sandstone, which may also represent the same group, and per- haps to some extent the basement bed of the London Clay.' LONDON CLAY This formation consists mainly of bluish-grey clay which weathers to a brown clay at and near the surface. It contains selenite, iron pyrites, and also nodular masses of argillaceous limestone or septaria, which were formerly dredged up at the entrance to the Orwell and Stour and burnt at Harwich for Roman cement. Some of these stones were used in old times for building purposes, as in Wrabness and Chel- mondiston churches and in the keep of Orford Castle. The London Clay is exposed beneath the Crag at Felixstow and Bawdsey, and the septaria are said to form rocky ground beneath the sea off the mouth of the Ore.^ The clay comes to the surface along the borders of the Deben below Woodbridge, along the Orwell and its tributaries below Burstall and Ipswich, and along the Stour and its tribu- taries below Boxford and Assington to the north of Nayland. The basement bed, from 8 to nearly 30 feet in thickness, comprises loamy sand with black flint pebbles and occasional sandstone with casts of shells. One of the most interesting sections was that at Kyson (Kingston) on the banks of the Deben about one mile below Wood- bridge, where teeth of the shark Odontaspis ('Lamna'), and also remains of Hyracotherium (formerly regarded as the remains of a monkey) were obtained.' The lower beds have also been exposed at Hadleigh brick- yard. The full thickness of the London Clay is nowhere developed in Sufl^olk because the formation has suffered extensive erosion. As much as 130 feet was proved in a well at Orford, about 68 feet at Southwold, and rather less than 50 feet at Leiston, the base of the London Clay occurring in Mr. Whitaker's opinion a little east of Saxmundham. Further south there was proved at Felixstow 64 feet of London Clay, at Trimley 88 1 feet, and at Stutton Hall 71 feet, the varying thickness being dependent locally on the elevation of the ground. The beds have been worked in places for the manufacture of bricks and tiles. The fossils of the London Clay include remains of turtles, of the sharks Otodus and Odontaspis, of the eagle-ray Myliobatis, the crab {Plagio- lophus) and the lobster {Hoploparia), as well as mollusca such as Nautilus and the boring shell Teredo, brachiopods, pyritized plants and fossil wood. Coprolites have also been met with. ' ' Geology of the Country around Ipswich,' etc., p. 15;' Geology of South-western Norfolk,' etc., Geol. Survey (1893), p. 163 ; and Geo/. Mag. (1895), p. 463. ' Capt. H. Alexander, 'Treatise on the Nature and Properties of the Soils of Norfolk, Suffolk and Essex' (1841), p. 15.
- Prestwich, ^art. Journ. Geol. Soc. vi. 272.
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