GEOLOGY system, while in lower levels of the present valleys, at Warren Hill east of Mildenhall and Redhill, both derived and contemporary implements are found.* The consideration of these old valley deposits is a subject which leads on to that of the origin of the present scenery. The main features over great part of England were sculptured prior to the Glacial period. The main features in Suffolk are of subse- quent date. Thus the Chalk escarpment in pre-Glacial times may have risen in Suffolk to heights comparable with those now found along the Chiltern Hills, the Dunstable and Royston Downs. It has in any case been considerably planed down, and excepting near Newmarket, where the ground rises to 275 feet, and at Mildenhall, its distinctive features have been obliterated. The widespread Glacial Drifts practically overwhelmed the county ; ice-action tended to smooth the inequalities of the land, though here and there a deep trough was excavated ; and the subsequent features have been carved out of the somewhat irregular accumulations of these erratic deposits, and partially out of the underlying strata. The melting of the ice led to torrential waters, which marked out some of the earlier valleys, and distributed masses of coarse gravel here and there. The erosion of the ground has revealed no traces of the earlier scenery ; indeed, over a great part of the county the thick drifts have not been intersected. Streams flow over them to join the main river courses which have cut deeply into the land. Subsequent depression, which took place no doubt slowly, has tended to arrest excavation, and the rivers widen, but, except in the higher courses, no longer deepen their channels. They have become sluggish, and in a few localities the hollows which were formed by estuarine action, or by the serpentine wanderings of the rivers, have been preserved as broads : tracts which are being slowly silted up and narrowed by the growth of marsh plants. Some of the broads, like Fritton Decoy and Oulton Broad, are held up by means of artificial embankments ; others, like those of Easton and Benacre, are barred by recent shingle. Small meres sometimes arise in areas where, owing to dissolution of the Chalk, the ground has subsided below the plane of saturation in that formation, as in the case of Barton Mere. The Alluvium, which forms level meadow or marsh land bordering the rivers, is one of the latest deposits, and may be said to be still in process of formation. It comprises deposits of varied character, but mainly silt and clay with peaty layers and gravel, altogether 20 to 30 feet in thickness. These low-lying tracts occupy a small area in north-western Suffolk, a part of the Bedford Level, itself a portion of the Fenland ; and strips of alluvium fringe the higher courses of the Lark and the Ouse. 1 Geol. Mag. (1902), p. 105. ^ See also Rev. O. Fisher, ^mt. Joum. Geol. Sec. xvii. 2. 27
