From still further south, at various points on the shores of the Bay of Biscay, and from the submerged peaty deposits which underlie the Landes, seeds have since been collected by my friend, Professor Jules Welsch, of Poitiers. These also all belong to common living British plants, except that at Brétignolles, south of latitude 47°, we meet for the first time one characteristic southern plant—the vine. Unfortunately the search for traces of man and his works in these deposits has so far been unsuccessful, and we cannot yet be certain therefore that they are all of quite the same date, or correspond exactly with the submerged forests of Britain.
CHAPTER VIII
SUMMARY
To what conclusions do the foregoing somewhat monotonous pages lead? Do they help us to explain the origin of our fauna and flora? What light do they throw on the antiquity of man in Britain, or on the race problems that everywhere confront us? Can the deposits therein described be in any way connected with written history or with legend? Do they give us any approach to a measure of geological time? And, to what extent does the period of the submerged forests tie on historical times with the Glacial Epoch?
All these questions are connected with the subject-matter of this little book; but it is not written with the idea of showing how much we know or pretend to know. Our main object is to draw attention to a much neglected period in geological history and to suggest directions in which further research is likely to be profitable. We have, however, made out several points, and can give an approximate answer to some of the questions.
It is quite clear that at the opening of the period with which this volume deals, the greater part of England stood fully 70 feet above its present level, for the oldest deposit we deal with is a land-surface covered with oak-forest and lying 60 feet below tide-level. The oaks cannot have flourished lower, but they may have grown on a soil well above sea-level. Perhaps taking the whole of the evidence into account, a subsidence of nearly 90 feet is the most probable measure of the extent of the subsequent movement.
We do not yet know whether in England this movement was a depression of the land or a rise of the sea; but the fact that the relative levels seem to have been quite different in Scotland and in Scandinavia seems to indicate that it was the land that moved, not the sea.
We begin, therefore, with a period when the whole of the southern part of the North Sea was an alluvial flat connecting Britain with Holland and Denmark, and to some extent with France. The Isle of Wight was connected with Hampshire, and the Channel Islands with France. Probably the Isles of Scilly were islands even then, for the channel between them and Cornwall is both deep and wide, though this may possibly be due to tidal scour.
The animals and plants yet known from this lowest submerged forest are disappointingly few; but the prevalence of the oak shows that the climate was mild, and that we have no clear indication of conditions approaching to those of the Glacial Epoch. In fact, in all the submerged forests the fauna and flora seem poor and monotonous, consisting essentially of living British species, with a few mammals since locally exterminated by man, and all known to have a wide range both in climate and latitude.
This in itself, however, is a point gained in the study of the origin of our flora; for though the deficiency is no doubt largely due to insufficient collecting, I am convinced that it is a true characteristic of this period of transition. Much time has been spent in examining and collecting the fossils of these submerged forests, and various friends have also worked at them; but everywhere we seem to get the same result, and many abandon the study because there is so little to show for it. The deposits certainly contain a much poorer fauna and flora than either the Pleistocene or the recent alluvial strata.
If we consider the Britain of the submerged forests as having lately emerged from a time when the climate was ungenial, we should naturally expect to find among the first incomers after the change only such animals and plants as have a wide climatic range or can migrate freely. It is these species, and these only, which will be living on the neighbouring lands; it is only an assemblage like this that can stand the climatic alternations and relapses that are likely to attend the transition. An assemblage consisting only of species widely distributed in latitude is probably an assemblage that has special means of dispersal—even if we do not happen yet to have discovered these means.