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Show 296 EOCENE PERIOD. [Ch. XXI. is often entirely wanting on the surface of the clay at the foot of the chalk escarpment, and no traces of chalk flint have evel' been found in the alluviun1 of the central district, or Forest ridge. It is rure, indeed, to see any wreck of the chalk, even at the distance of two or three miles from the escarpments of the North and South Downs. 'I'o this general rule, however, an exception occurs neal' Darcombe, about three miles to the north of Lewes, ~vherc we obtain the accompanying section*. No. 71. :: .. .__-=_=_-·:·.:·::;·::·. Barct/1/IUC ~ ~~~~~~~~ ~: ~ 1 __.l ~- :;~~~ Scctionf1'om tlw 1V01·th escarpment of the South Downs to Barcombc. 1, Gravel composed of 11artially-ronnded chalk flints. 2, Chalk with ancl without flints. 3, Lowest chalk or chalk marl (upper green-sand wanting). 4 1 Gault. 5, Lower green-sand. 6, ·weald clay. It will be seen that the valley at the foot of the escarpment extends, in this case, not only over the gault, but over the 'lower green-sand' to the Vveald clay. On this clay a thick bed of flints, evidently derived from the waste of chalk, remains in the position above described. We say that there is no detritus of the chalk and its flints on the central ridge of the Weald. I have sought in vain for a vestige of such fragments, and Mr. Mantell, who has had greater opportunities of minute investigation, assures me that he has never been able to detect any. Now whether we embrace or reject the theory of the former continuity of the chalk and othet· groups over the whole space intervening between the North and South Downs, we cannot certainly imagine that any transient and tumultuous rush of waters could have swept over this country, which should not have left some fragments "' The author villitcd this locality with Mr. Mantell, to whom he is indebted for tbis section. Ch. XXI.J . ALLUVIUM OF WEALJJ VALLEY. 291 of the chalk and its flints in the deep valleys of the Forest ridge. Indeed, if we adopted the diluvial hypothesis of Dr. Buckland, we should expect to find vast heaps of broken flints drifted more frequently into the valleysofthe Gault and Weald clay, instead of being so frequently confined to the summit of the chalk downs. On the other hand, it is q uitc conceivable that the slow agency of oceanic currents may have cleared away, in the course of ages, the matter which fell into the sea from wasting cliffs. The reader will recollect our account of the manner in which the sea has advanced, within the last century, upon the Norfolk coast at Sherringham *. a, Crag. No. 72. Section of clijf11 west of Sherringham. b, Ferruginous flint breccia on the surface of the chalk. c, Chalk with flints. The beach, at the foot of the cliff, is composed of bare chalk with flints, as is the bed of the sea near the shore. No one would suspect, from the appearance of the beach at low water, that a few years ago beds of solid chalk, together with sand and loam of the superincumbent crag, formed land on the very spot where the waves are now rolling; still less that these same formations extended, within the last 50 years, to a considerable distance from the present shore, over a space where the sea has now excavated a channel 20 feet deep. As in this recent instance the ocean has cleared away part of the chalk, and its capping of crag, so the tertiary sea may have swept away not only the chalk, but the layer of broken flints on its surface, which was probably a marine alluvium of the "' Vol. i. p. 268, and Second Edition, p. 307, |