Among the nine species of beetle determined by Mr G. C. Champion it is noticeable that two belong to sandy places. This suggests that the fen may have had its seaward edge protected by a belt of sand-dunes, just as the coast of Holland is at the present day.
This submerged forest in the middle of the North Sea has been described fully, for it raises a host of interesting questions, that require much more research before we can answer them. A sunken land-surface 60 feet and more below the sea at high-tide corresponds very closely with the lowest of the submerged forests met with in our dock-excavations. But if another bed of peat occurs at a depth of 130 or 140 feet at the Dogger Bank, this would be far below the level of any recently sunk land-surface yet recognised in Britain. Also, if the slabs of very modern-looking peat, containing only plants and insects still living in Britain, come from such a depth, out of what older deposit can the Pleistocene mammals, such as elephant, rhinoceros, and hyaena, have been washed?
These questions cannot be answered conclusively without scientific dredging, to fix the exact positions and depths of the outcrops of moorlog. When we remember also that beneath a submerged forest at about the depth of the Dogger Bank there was found at Tilbury, in the Thames Valley, a human skeleton; and that both human remains and stone implements have been discovered in similar deposits elsewhere, we can point to the Dogger Bank as an excellent field for scientific exploration.
The Dogger Bank once formed the northern edge of a great alluvial plain, occupying what is now the southern half of the North Sea, and stretching across to Holland and Denmark. If we go beyond the Dogger Bank and seek for answers to these questions on the further shore, we find moorlog washed up abundantly on the coasts of both Holland and Denmark, and it has evidently been torn off submerged ledges like those of the Bank. Numerous borings in Holland give us still further information, for they show that beneath the wide alluvial plain, which lies close to the level of the sea, there exists a considerable thickness of modern strata. At Amsterdam, for instance, two beds of peat are met with well below the sea-level, the upper occurring at about the level of low-tide, the lower at a depth of about 50 or 60 feet below mean-tide. That is to say, the lowest submerged land-surface is found in Holland at just about the same depth as it occurs in England, and probably on the Dogger Bank also.
Below this submerged land-surface at Amsterdam are found marine clays and sands, which seem to show that the lowest “continental deposit,” as it is called by Dutch geologists, spread seaward over the silted-up bed of the North Sea; but no buried land-surfaces have yet been found below the 60-foot level anywhere in Holland.
This appearance of two distinct and thick peat-beds, underlain, separated, and overlaid by marine deposits, seems to characterise great part of the Dutch plain. It points to a long period of subsidence, broken by two intervals of stationary sea-level, when peat-mosses flourished and spread far and wide over the flat, interspersed with shallow lakes, like the Norfolk broads.
The enclosed and almost tideless Baltic apparently tells the same story, for at Rostock at its southern end, a submerged peat-bed has been met with at a depth of 46 feet.
On passing northward into Scandinavia we enter an area in which, as in Scotland, recent changes in sea-level have been complicated by tilting, so that ancient beach-lines no longer correspond in elevation at different places. The deformation has been so great that it is impossible to trace the submerged forests; they may be represented in the north by the raised beaches, which in Norway and Sweden, as in Scotland and the north of Ireland, seem to belong to a far more recent period than the raised beaches of the south of England. It seems useless to attempt to continue our researches on submerged forests further in this direction, especially as during the latest stages, when we know England was sinking, Gothland appears to have been slowly rising. Those who wish to learn about the changes that took place in the south of Sweden should refer to the recent monograph by Dr Munthe.
CHAPTER V
THE IRISH SEA AND THE BRISTOL CHANNEL
On the west coast of Scotland, as on the east, the succession of events seems to have been quite different from that which can be proved further south. It looks as though we must seek for equivalents of our submerged forests in certain very modern looking raised beaches and estuarine deposits, such as those of the Clyde. Even when we move southward to the Isle of Man deeply submerged post-glacial land-surfaces appear to be unknown, though there is evidence of a slight sinking, and roots of trees are found a few feet below the sea-level. In the Isle of Man we still come across the modern-looking raised beaches so prevalent in Scotland though unknown in England.