A HISTORY OF SUSSEX overspread the clays, or the bare heaths which characterized the sands. The areas occupied by Chalk were probably in prehistoric times, and even much later, the most settled and highly civilized parts of Britain ; they are certainly the areas over which are found our finest and most extensive prehistoric antiquities. We in Sussex scarcely realize how peculiar and abnormal a deposit is this soft pure white limestone known as Chalk. It occupies a small part of western Europe, but in other regions of the world there is nothing very closely resembling it, except in comparatively thin beds. This thousand feet of strata is composed almost entirely of marine organisms — either recognizable or decayed — except in the lower part, in which there is a considerable admixture of clay and other detritus washed from the land. The rest of the formation is so uniform that the differences are not such as to strike the casual observer, who would describe the whole mass simply as chalk. On examining more closely we find at different levels slight differences in the character of the deposits and in their included fossils. These variations extend throughout the county, so that it is usually possible from an isolated chalk pit to tell approximately how high we are above the base of the deposit.^ The lower part of the Chalk consists essentially of greyish marl In alternate hard and soft beds, which make conspicuous ledges on the fore- shore and at the base of the cliff between Eastbourne and Beachy Head. These deposits form the Lower Chalk, which has a thickness of from 150 to 200 feet, and occupies the gently rising ground at the foot of the Chalk escarpment. Its soil is more retentive than that of the rest of the Chalk, and much of it was formerly woodland, though now it is mainly under the plough or changing to permanent pasture. The fossils are pecuHar. Towards the base we find a narrow zone of hard sandy chalk with quartz grains and occasional phosphatic nodules. This zone is characterized by the small sponge Staiironema carteri. Then follow marls, breaking up into pieces with curved faces and containing Ammonites varians, A. rotomagensis, Scapbites cequalis, and Holaster subglobosus^ as well as numerous bivalves and fish. Most of the beautifully-preserved fish remains found at Lewes and to be seen in every museum come from this division. At the top of the Lower Chalk is a band 10 or 20 feet thick of softer, darker, and more impervious marl, known as the ' Belemnite Marl,' from its characteristic fossil Actinocamax {Belemnitclhi) plenus. This marl holds up and throws out the water which falls on the higher beds of chalk ; many of the springs are therefore given out at the junction of the Lower with the Middle Chalk. Very little water is obtained from the Lower Chalk itself, except where it is much shattered, as near Eastbourne. This division of the Chalk, besides forming land of different agricultural character, produces hydraulic lime, which cannot be made from the beds above. There is a sudden change from the soft Belemnite Marl to the hard
- The best account of the zones will be found In Dr. A. V. Rowc, 'The Zones of the White
Chalk of the English'Coast : I. — Kent .ind Sussex,' Proc. Geo/. Auor. vol. xvi. pt. 6 (1900). 10
