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The contents of the Norwich Crag (see p. 244) plainly show that the rivers which entered the shallow sea came from the westward and carried débris which had been derived from the central parts of England. From the great depth of the Crag at Southwold (147 feet), and at Beccles1 (80 feet), where the muddy nature of the deposits is also remarkable, we might suppose that one of these rivers traversed what is now the valley of the Waveney, this being continued westward into that of the Little Ouse, which may then have been occupied by a river coming from the region of Bedford and Bucks, where the Ouse now takes its rise. This stream, however, could hardly have carried the Carboniferous fossils which have been found in the Crag, and unless these were drifted along the coast from some far northern locality, Derbyshire and Leicestershire are the nearest and most probable sources. valley of the Trent at once suggests itself as a possible channel of transport, for we know that the ancient course of this river was not that which it now follows, but through the Jurassic escarpment along the valley now occupied by the Witham into the basin of the Wash.2 Further, its drainage system is such that its tributaries could derive all the stones which have been recorded as occurring in the Norwich Crag.

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Bearing in mind these facts and the general considerations mentioned on p. 254, there is nothing improbable in the suggestion that the breach in the Chalk escarpment which is now occupied by the Wash was initiated by the combined forces of the rivers Trent, Witham, Welland, and Nen, before this escarpment had receded to anything like its present position. There is every reason to suppose that in later Pliocene time all these rivers traversed the

1 Woodward, "Geology of the Country around Norwich," p. 156. 2 See “Quart. Journ. Geol. Soc.,” vol. xxxix. p. 606, and “Geology of the Country around Lincoln," Mem. Geol. Survey.

Jurassic ridge, although only two of them (the Welland and Nen) now retain their ancient channels, and we may fairly assume that the bay of the Wash did not then exist, but that the combined streams of the above-mentioned rivers occupied a broad valley which passed along or just outside the northern coast of Norfolk, and opened into an estuary somewhere to the north-east of that county (see Plate XIII.). That a river of some size did at a much later date pursue such a course has been surmised from the peculiar geological features presented by the northern coast of Norfolk. This coast is bordered by a continuous strip of alluvium, the western part of which rests on boulderclay which is banked against a steep slope of chalk. Referring to the alluvium, Mr. H. B. Woodward remarks,' "the physical characteristics of the area suggest that this low ground was originally an old river-valley, and that the heights which bordered it on the north have been destroyed by the ravages of the sea."

Passing now from these details of the Pliocene riversystem, let us consider what other changes may have been caused by the depression which led to the formation of the North Sea. The most direct and important change was the submergence of the land which had hitherto from the commencement of Tertiary time united Scandinavia with Scotland and Iceland. Not only did this depression open a communication with the Arctic Ocean, but in all probability with the North Atlantic also, by the temporary breaching of the isthmus between Scotland and the Faroe Islands, and by the conversion of the deep valley or hollow north of these islands into a strait. By these passages many North Atlantic and American species of mollusca gained access to the Anglo-Belgian part of the Pliocene Sea, no fewer than eighteen American species occurring in 1 "Geology of the Country around Fakenham," Geol. Surv. Mem.,

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the newer Crags, only seven of which still live on the Scandinavian coast, the remainder being now confined to the North American region.

This view of late Pliocene geography is represented on Plate XIII., and this differs from previous restorations chiefly in those particulars where recent information has afforded more correct data than were formerly available. The first attempt to give an outline of Pliocene geography was by Mr. Godwin-Austen, who, in 1866, published a map on which the supposed area of "the Crag Sea" was delineated. At that time, however, it was unknown that the sands of the Coralline Crag ranged so far south and to such a high level; while many deposits were then called Crag which have since been proved to be of Pleistocene age; consequently, his map combines portions of the geographical conditions of several distinct periods, and is not correct for any one portion of them.

Professor Boyd Dawkins has given a map of Pliocene Britain which may be taken as an approximation to that of the later portion of the period, but since its publication Mr. Jamieson has shown that the supposed Crag of Aberdeen is a remanié deposit of Pleistocene age,' and consequently there is no proof of the Red Crag sea having touched any part of the Scottish coast. In the region of the Faroe Islands, also, Professor Dawkins shows a greater area of water than I deem probable; for it should be remembered that the whole of the newly-formed North Sea may have been very shallow. No deep-sea deposits of Pliocene age have yet been found in north-western Europe, and the phenomena of the Forest Bed show that a very slight upheaval was sufficient to convert a large area of it into dry land.

1 "Quart. Journ. Geol. Soc.," vol. xxii. p. 240.

2Early Man in Britain," 1880, p. 73.

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Quart. Journ. Geol. Soc.," 1882, vol. xxxviii. p. 145.

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PLATE XIII.

GEOGRAPHY OF THE NEWER PLIOCENE EPOCH. The closer lines representing sea-areas at the time of the Forest Bed.

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