114 



NA TURE 



[June 2, 1904 



There is no similar series of well marked submerged 

 valleys on the floor of the North Sea from which to estimate 

 the amount of submergence of that tract, at least half of 

 which, at no very distant date, formed a land-surface that 

 connected Britain with the rest of the Continent. The 

 charts show this sea-floor to consist of two distinct portions. 

 The northern half forms a plain, which appears to slope 

 gradually towards the north. The southern half, however, 

 rises somewhat rapidly from the edge of that plain into an 

 escarpment that runs in a north-easterly direction for a 

 distance of 500 miles, from off Flamborough Head to the 

 Skagerrak. From the top of this escarpment the surface 

 undulates southward as a higher submarine plain, traversed 

 by the still feebly traceable submerged valleys of the Elbe, 

 the Rhine, and the Thames, and covering an area of more 

 than 50,000 square miles. An uprise of not more than 

 300 feet would turn this tract into a rolling plateau of dry 

 land, like the downs and wolds of Yorkshire, which are 

 its emerged continuation. Such an amount of uplift 

 would probably be amply sufficient for the transaction of 

 all the later geological history of the region. The con- 

 version of the area into a sea-bottom may not have been a 

 continuous process. It was probably in operation during 

 the early stages of the Glacial period, and its latest phases 

 come down at least into Neolithic time. 



(2) The sheets of peat with stools and trunks of trees, 

 known as sunk or submerged forests, and of such frequent 

 occurrence around the coasts of the British Isles, have long 

 been confidently regarded as proofs of recent subsidence of 

 the land. That they generally mark former land-surfaces 

 cannot be doubted, for the tree stumps are seen to send 

 their roots down into the soil underneath, and manifestly 

 stand in the places where they originally grew. The 

 presence of hazel-nuts, elytra of beetles, land-snails, and 

 other terrestrial organisms, affords further confirmation of 

 this conclusion. The great majority of these vegetable 

 accumulations are found between tide-marks in bays and 

 estuaries, and in many cases they can be seen to pass below 

 the limits of the lowest tides, and thus to be constantly 

 in part submerged. The trees and the fresh-water plants 

 must have lived above the reach of the sea, so that they 

 now lie 20 feet or more below the level at which they 

 originally grew, and the conclusion has been drawn that 

 they mark a general subsidence of these islands, to the 

 amount of at least 20 feet, at a comparatively recent date. 



Sir Archibald Geikie was inclined to believe that this con- 

 clusion has been rather too sweepingly drawn. That some 

 of the submerged forests may be satisfactorily accounted for 

 without any change in the level of the land or of the sea was 

 urgently enforced more than eighty years ago by John 

 Fleming, in reference to the examples first brought to 

 notice by him in the estuaries of the Tay and the Forth. 

 It will be readily understood that, in the later .stages of 

 the Glacial period, when much detritus was swept off the 

 land into the sea, the conditions would probably be especiallv 

 favourable for the formation of alluvial bars along our 

 coasts, such as are now in course of accumulation for 

 hundreds of miles on the southern coast of Iceland, where 

 some of the features of that period may still be said to 

 linger. Behind these barriers lagoons would arise, 

 which in course of time might become marshes, and 

 eventually peaty flats, supporting a growth of trees. But 

 when the supply of sediment failed, and the sea, instead of 

 heaping up the bars, began to breach them, the level of the 

 bogs would sink by the escape of their water to the beach, 

 and the tide at high-water would overflow and kill off the 

 forests. Occasionally, owing to the action of underground 

 drainage, the seaward margins of forest-covered peatv flats 

 may have been detached from the main bodv and launched 

 downward on the beach, even beneath low-water mark. 



Had our littoral sunk forests been confined to a few places 

 where the topographical conditions were specially favour- 

 able for their production, we may concede that they would 

 not in themselves furnish sufficient proof of a shift of level, 

 either on the part of the land or of the sea. But when we 

 consider their widespread distribution all round the margin 

 of these islands, even on those shores where it is difficult 

 to believe that there has been any subsidence or slipping 

 downward of a land-surface owing to the draining off of 



NO. 1805. VOL. 70] 



underground water, we may well doubt whether the old 

 belief should be disturbed, that the facts, taken as a whole, 

 prove a general submergence. 



Fortunately, the evidence available on this subject allows 

 us to go a step farther. We need not be content with such 

 debateable proofs as are furnished by the sunk forests 

 between tide-marks, for land-surfaces can be adduced which 

 are buried beneath marine accumulations in circumstances 

 that leave no doubt as to the facts of submergence. 



The author, after presenting some details proving sub- 

 mergence at Belfast, at Hull, and at Grimsby, to the extent 

 of sometimes as much as 52 feet, stated that on the coast 

 of South Wales interesting sections had been laid open in 

 the excavation for the Barry Docks, in Glamorgan, furnish- 

 ing conclusive proof of a succession of at least four layers 

 of peat overlain by estuarine deposits, and in a situation 

 which precludes any recourse to local settlement by drainage 

 of underground water or downward slipping. The strata 

 are manifestly undisturbed, and the lowest is an unmis- 

 takable land-surface. It consists of peat full of remains of 

 oak, hazel, cornel, hawthorn, and willow, together with 

 crushed shells of Hyalinia and, apparently, Pisidium and 

 Planorbis. The soil underneath this forest-growth has 

 yielded specimens of Helix, Hyalinia, Succinea, Limneea, 

 Tupa, and \'alvata. This buried forest-growth lies at a 

 depth of 35 feet beneath Ordnance-datum, or 55 feet beneath 

 the line of high-water of ordinary spring tides. It proves 

 a submergence of at least 55 feet, and the peat-bands at 

 higher levels mark successive pauses in this submergence. 

 That the movement was in progress in Neolithic lime may 

 be concluded from the occurrence of a portion of a polished 

 celt in the uppermost layer of peat, from which also two 

 bone needles are reported to have been obtained. Mr. 

 Strahan informed the author that, wherever excavations have 

 been made at the mouths of the valleys on the coast of South 

 Wales, similar layers of peat have been cut through at 

 depths below low-water mark. It would thus appear that 

 the submergence has been general all along the coast-line. 



On the southern English coast similar evidence of a 

 considerable change of level has long been known. During' 

 the extensive excavations for new dock accommodation at 

 Southampton, a bed of peat, 10 feet thick, has been found, 

 descending to a depth of 43 feet below Ordnance-datum. 

 This vegetable accumulation has yielded many land and 

 fresh-water shells ; abundant trunks of oak with roots, 

 sometimes 2 feet long, passing down into the loam beneath ; 

 plentiful remains of beech and hazel, together with some 

 birch and pine. The plants also include bulrush, sedge, 

 bog-myrtle, heaths, and bracken. From this bed, bones, 

 horn-cores, and part of the skull of Bos primi genius were 

 obtained ; likewise horns and bones of red deer, tusk of 

 boar, bones of hare, and horn of reindeer. Traces of man 

 were found in the same deposit, as shown by the occurrence 

 of dark flint-flakes, a round perforated hammer-stone, and 

 a fine bone needle polished by use. 



There is thus evidence of a comparatively recent sub- 

 mergence of the south-west of England to the extent of at 

 least 50 or 60 feet. We are probably justified in considering 

 the present position of the Glacial raised beach in Gower 

 as a further indication of the same movement, and there 

 seems no reason why we should not connect the evidence 

 of this beach with that of the terrace lately detected in 

 Cork. If these tracts are included in our survey, we see 

 that the submergence probably stretched across South Wales 

 and St. George's Channel to the south of Ireland. The 

 evidence from Hull and Grimsby, which shows that a similar 

 marked submergence has taken place along part of the 

 east coast, not improbably indicates that the change of 

 level extended across Wales and the centre of England. 

 This submergence appears to be the latest in the long 

 series of oscillations which have affected the southern 

 portions of our islands. No proof has yet been obtained 

 that so serious an amount of recent submergence has ex- 

 tended farther north. In the northern tracts the latest 

 recorded change of level has been an emergence of the 

 land in Neolithic time. 



(iii.) Bearing of the Evidence on the Causes of Emergence 

 and Submergence. — In conclusion, the author pointed out 

 the inferences that appeared to him to be deducible from the 



