Though mammalian bones are now so seldom found, whenever the sand-banks shift slightly, as they tend to do under the influence of tides and currents, the edges of the submerged plateau are laid bare, exposing submarine ledges of moorlog, which still yield a continuous supply of this material. Messrs. Whitehead and Goodchild have recently published an excellent account of it, having obtained from the trawlers numerous slabs of the peculiar peaty deposit, with particulars as to the latitude and longitude in which the specimens were dredged. Mrs Reid and I have to thank the authors for an opportunity of examining samples of the material, which has yielded most interesting evidence as to the physical history, botany, and climatic conditions of this sunken land. The following account is mainly taken from their paper and our appendix to it.
We are still without information as to the exact positions of the submarine ledges and cliffs of peat from which the masses have been torn; but there seems little doubt that some of them were actually torn off by the trawl. One block sent to me was full of recently dead half-grown Pholas parva, all of one age, and must evidently have been torn off the solid ledge. Pholas never makes its home in loose blocks. We unfortunately know very little about the natural history of the boring mollusca and their length of life. If, as I think, this species takes two years to reach full growth, then it is evident that the ledge of moorlog full of half-grown specimens must have been exposed to the sea continuously for one year, but not for longer. It ought also perhaps to tell us the depth of water from which the mass was torn; but nothing is known as to the depth to which Pholas may extend—it has the reputation of occurring between tide-marks or just below, but it may extend downwards wherever there is a submarine cliff.
Though we are still unable to locate exactly these submarine ledges or fix their depth below the sea, the blocks of moorlog are so widely distributed around the Dogger Bank, and have been dredged in such large masses, that it seems clear that a “submerged forest” forms part of the core of the bank. As nothing else approaching to a solid stratum appears to be dredged over this shoal, we may assume that the moorlog forms a sort of cap or cornice at a depth of about 10 fathoms, overlying loose sandy strata, and perhaps boulder clay, which extend downward to another 10 fathoms, or 120 feet altogether. Unfortunately we cannot say from what deposit the large bones of extinct animals were washed; they may come from the sands below the moorlog, but it is quite as probable that the Pleistocene deposits formed islands in the ancient fen—as they do now in East Anglia, Holderness, and Holland.
More than one submerged forest may be present on the Dogger Bank. The masses of moorlog are usually dredged on the slopes at a depth of 22 or 23 fathoms; but at the south-west end it occurs on the top as well as on the slope, the sea-bottom on which the moorlog is found consisting of fine grey sand, probably an estuarine silt connected with the submerged forest, for the North Sea sand is commonly coarse and gritty.
With regard to the moorlog itself and its contents, it is possible that some of the mammals in the list, such as the reindeer, beaver, and walrus, may belong to this upper deposit; but we have no means of distinguishing them, as the bones were all found loose and free from the matrix. The insects and plants were all obtained from slabs of this peat.
The dredged cakes of peat handed to us for examination came from different parts of the Bank; but they were all very similar in character, and showed only the slight differences found in different parts of the same fen. The bed is essentially a fen-deposit of purely organic origin, with little trace of inorganic mud. It is fissile and very hard when dry, and in it are scattered a certain number of fairly well-preserved seeds, principally belonging to the bog-bean. Other recognisable plant-remains are not abundant. They consist of rare willow-leaves, fragments of birch-wood and bark, pieces of the scalariform tissue and sporangia of a fern, and moss, and, curiously enough, of groups of stamens of willow-herb with well-preserved pollen-grains, though the whole of the rest of the plant to which they belonged had decayed.
The material is exceptionally tough, and is very difficult to disintegrate. In order to remove the structureless humus which composed the greater part of the peat, we found it necessary to break it into thin flakes and boil it in a strong soda solution for three or four days. Afterwards the material was passed through a sieve, the fine flocculent parts being washed away by a stream of water, the undecomposed plant remains being left behind in a state for examination. These remains were mixed with a large amount of shreds of cuticle, etc., but recognisable leaves were not found in the washed material.
The general result of our examination is to suggest that the deposit comes from the middle of some vast fen, so far from rising land that all terrigenous material has been strained out of the peaty water. The vegetation, as far as we have yet seen, consists exclusively of swamp species, with no admixture of hard-seeded edible fruits, usually so widely distributed by birds, and no wind-borne composites. The sea was probably some distance away, as there is little sign of brackish-water plants, or even of plants which usually occur within reach of an occasional tide; one piece however yielded seeds of Ruppia. The climate to which the plants point may be described as northern. The white-birch, sallow and hazel were the only trees; the alder is absent. All the plants have a high northern range, and one, the dwarf Arctic-birch, is never found at sea-level in latitudes as far south as the Dogger Bank (except very rarely in the Baltic provinces of Germany).
The plants already found are:—
| Ranunculus Lingua | Betula alba |
| Castalia alba | ” nana |
| Cochlearia sp. | Corylus Avellana |
| Lychnis Flos-cuculi | Salix repens |
| Arenaria trinervia | ” aurita |
| Spiraea Ulmaria | Sparganium simplex |
| Rubus fruticosus | Alisma Plantago |
| Epilobium sp. | Potamogeton natans |
| Galium sp. | Ruppia rostellata |
| Valeriana officinalis | Scirpus sp. |
| Menyanthes trifoliata | Carex sp. |
| Lycopus europaeus | Phragmites communis |
| Atriplex patula |