by Grant Allen
Moreover, when Britain was repeopled after the great ice age, it must have been united to the Continent somewhere, or else it could not possibly possess the large number of European plants and animals which it actually contains. Had it then been an island, it might have had a considerable population of ferns and small-seeded flowers, of birds and winged insects, blown over to it from the shores of France or Holland; it might even have had a fair sprinkling of snails and lizards, or a few small quadrupeds, wafted across on logs of wood, or carried over accidentally by various chances; but it would be quite impossible that it should have all the species of large or middle-sized wild mammals which we see now inhabiting it — the red deer, the fallow deer, the otter, the badger, the fox, the hare, the rabbit, the weasel, the stoat, the marten, the hedgehog, the wild cat, the mole, the shrew, the squirrel, and the water-vole. Altogether, we have no less than forty species of British mammals; while the bear, the wild boar, the beaver, the reindeer, and the wolf have become extinct within the historical period; and the wild white cattle even now survive sparingly in Chillingham Park and a few other scattered places. Clearly, as none of these animals or their ancestors can have been in Britain 80,000 years ago, they must have come into Britain at some later date, across a wide bridge of solid land. For Mr. Wallace has conclusively shown that islands which have never formed part of a mainland never have any terrestrial mammals at all; and that a very narrow strait is quite sufficient to prevent the passage of mammals from one island to another. The sound which divides the Indo-Malayan region from the Australian region is hardly wider than that which separates England from France; yet not one single Australian mammal has ever reached the Indo-Malayan region, and not one single Indian mammal has ever reached Australia. The kangaroos, wombats, phalangers, and cassowaries of the one district are quite distinct in type from the elephants, tapirs, tigers, deer, and monkeys of the other. So that our numerous existing English fauna must certainly have crossed over on dry land.
We may take it for granted, then, that the mass of British plants came in, from the east and south-east, immediately after the ice of the glacial epoch had passed away. For the ice had driven man and beast, herb and tree, southward before it; and even if there was a little fringe of what is now Southern Britain not wholly glaciated, yet its condition must have been like that of the little habitable fringe in Greenland, and its plants and animals (if any) must have been of thoroughly Arctic types. But as the glaciers cleared away again, with the return of the sun to the northern hemisphere after its long cold cycle, the southern and eastern plants and animals must have followed the retreating ice-sheet from year to year; till at last the species which used to inhabit Kent and the Isle of Wight found their permanent home in Lapland, and those which used to inhabit Greece and Italy found their permanent home in Holland, Denmark, and Great Britain.
This sufficiently accounts for the presence in England and Scotland of the central European and Scandinavian elements; but it does not account for the presence of my hairy spurge and of all the other south-western species, belonging to the Pyrenean and Italian region. Clearly, the ordinary plants of Eastern England are plants which once spread uninterruptedly from Warwickshire to Central Europe, when the belt of land over the German Ocean was still entire; and clearly, too, the ordinary plants of the North and of Scotland are plants which once spread uninterruptedly from Yorkshire to Scandinavia, during the same period; while both classes have been afterwards isolated in Britain by the gradual subsidence of the intervening land. But this still leaves unanswered the question, Whence did we get the Pyrenean types?
Perhaps one might be disposed at first sight to fancy that they came over separately, as we know a few American plants have really done. There is the well-known Canadian canal weed, which was introduced by a botanist into a tank near Cambridge in 1845, and rapidly spread over all England; there are a few orchids and other wild flowers whose seeds have apparently been carried across the Atlantic on the feet of birds; and there are some half-dozen escaped garden flowers, like the evening primrose, which have established themselves easily among some rare warm spots in our congenial climate. Possibly it might seem as though the arbutus, the hairy spurge, the Mediterranean heath, and all the rest of the southern species in South-Western England or Ireland had got across to us in somewhat the same fragmentary fashion, and had succeeded in effecting a foothold only in these warmer Cornish and Irish nooks. But there are a great many reasons against believing this. In the first place, we have the immense number to account for — at least ninety species, all told; which is a prodigious item to set down to the chapter of accidents. For the distance from Bordeaux to Kerry is really 700 miles, while the distance from Portugal to the Azores (which are peopled with plants and animals in the most fragmentary manner) is only 900; and we can hardly suppose that so large a number of southern plants could permanently establish themselves (against the prevailing winds) in a country already occupied by a flourishing native flora. But two more fatal objections are these: First, our southern plants are only found in the extreme south-west, and not in the warmest parts of the Isle of Wight, of Kent, or of Hampshire. Even at Bournemouth and Ventnor we meet with none of them. And secondly, they are all evidently dying out; they represent an old flora which is no longer adapted to the country, not a new flora pushing its way vigorously into regions occupied by less congenial plants. Every year they are disappearing before our very eyes, and many of them are from time to time now being expunged from our floras. The Kilmington lobelia is getting rarer as every summer passes; the wild asparagus, once common on the Lizard promontory, is now only to be picked, at the imminent risk of life and limb, amongst the crannies of a rocky islet at Kynance Cove; the purple viper’s-bugloss has been driven to the very extremity of Britain at Penzance; while the various kinds of rock-cistus, the Steep Holme pæony, and the Cheddar pink linger on each only in a single inaccessible spot in the south-western peninsula of England. These are clear evidences that they form the last stragglers of a vanquished flora, not the vigorous vanguard of a victorious and aggressive race.
And now we are in a position fairly to settle the problem where the hairy spurge and its fellows have come from, and how they got here. People who recognise the fact that Britain was once joined to the Continent are too apt to fancy that it was joined only by a sort of narrow bridge between Dover and Calais. The aspect of the shore on either side, the high bluffs of Shakespeare’s Cliff and Cap Grisnez, the geological continuity between the chalk and the other formations on the two coasts, all forcibly suggest that France and England must once have been joined there — as, indeed, they undoubtedly were. But we are all inclined mentally to minimise the amount of connection; we stick in an isthmus just sufficient to carry the South-Eastern Railway across to Boulogne, and then we are fully satisfied with our new geography. In reality, however, the old land connection was something far more complete and universal than that. There is every reason to believe that, at the close of the last glacial epoch, Great Britain and Ireland formed a part of the Continent, not in the sense in which Scandinavia or Denmark still does, but in the sense in which Bavaria and Switzerland still do. The land of Europe then stretched out to seaward far beyond Ireland, Spain, and the Faröe Islands; and Cork, Glasgow, and Liverpool then stood further inland than Lyons, Munich, and Geneva stand at the present day.
Walking one morning a few winters since — just after the most terrible tempest of recent years — on the Parade at Hastings, I happened to notice a curiously shaped flint among the shingle lately thrown up by the great storm. The waves had beaten right over the sea-wall, and scattered a litter of wrack and pebbles along the whole roadway. I stooped down and picked up the odd-looking fragment: to my surprise, I found it was a palæolithic implement, a rudely chipped flint knife of the older stone age, the relic of a race compared with whom even the builders of Wansdyke here were men of yesterday. This rude flake was fashioned by the naked black-fellows who hunted the rhinoceros and the mammoth in the E
nglish valleys, before ever the great ice age itself had spread its glaciers over the length and breadth of the land, a couple of hundred thousand years since. Its outer surface was dulled and whitened by age, as is always the case with these primæval flint weapons; but its edge was still sharp and keen, though crusted in places with a hard film of mineral deposit, and also blunted here and there by use in cutting clubs and reindeer bones for its savage possessor. But there were no traces of rolling as in water-worn pebbles: the knife was freshly disinterred. It was clear that the storm had just unearthed it from beneath the submerged forest which belts all the coast from Beachy Head to Dungeness. For the forest is a post-glacial deposit; and it once formed part of this great connecting land, now buried beneath the Atlantic, the English Channel, and the German Ocean. The trees which composed it still stand as upright stumps, firmly bedded in a layer of tenacious clay; and strewn beneath them lie prostrate boles, in the very place where the wind threw them down some fifty or sixty thousand years ago. In the public garden at Hastings, one of these huge balks, dug up on the St. Leonard’s beach, has been fixed as a curiosity; and, though its outer layer is charred and blackened by the water, the inner wood is still as sound and as firm as on the day it fell. We have to deal here with a time which is marvellously ancient indeed when measured by our ordinary human and historical chronology, but which is quite modern when judged by the vast timepiece of cosmical and geological cycles.
All round the coast of England you will find endless traces of these submerged forests, especially wherever the land shelves off slowly to seaward. That most lively of mediæval travellers, Giraldus Cambrensis (whose amusing and somewhat slangy diary would be much more read, I am sure, if people did not incongruously mistake him for a dry chronicler of the monastic sort), gives a full and really scientific account of one which he came across in the course of his Welsh peregrinations; and ever since his time the submerged forests have been noted in spot after spot in every part of Southern Britain. Beginning in the great bight between Wales and Scotland, they continue round the coast at Holyhead; turn up again in Cardigan Bay; fringe the whole Bristol Channel; fill in the bottom of the fiords at Falmouth, Dartmouth, Torquay, and Exmouth; trend round the Isle of Wight, Selsea, and Pevensey Bay; appear sparingly off the Essex coast; and thence run up by Cromer and the Wash to Holderness and Lindisfarne. They are everywhere newer than the glacial deposits, and so they give us a fair ground for believing that a great general subsidence of the land has taken place all round the shore of England at a comparatively recent period — that is to say, since the close of the last glacial epoch. How recent they are is well shown by the nature of the remains themselves; for they often contain undecayed leaves, water-logged hazelnuts, bits of small twigs, and other forestine rubbish of a perfectly undecayed and modern-looking character. Some of the twigs even break with a sharp crackling sound, like dry wood freshly taken from a modern forest.
Fig. 16. — Sketch Map of Post-Glacial Britain.
The question now remains, If the land once thus extended farther out to sea than at present, how far out did it extend? or, in other words, how large a subsidence has taken place? Here we have an excellent hint for our guidance in the fact that Ireland must have been united to England since the glacial epoch, because we find in Ireland a large proportion of the British plants and animals, including a considerable number of land mammals. Now, how much must we raise the general land surface of the British Isles in order to unite Ireland to Great Britain? Well, a rise of less than one hundred fathoms would suffice to join the whole of our islands throughout nearly all their length, leaving only two large lakes in the very deepest parts of the sea, where the plummet marks a depth of a hundred and fifty fathoms. One of these two large lakes would lie between Galloway and Ulster, and the other would fill up the hollow of the Minch between the Hebrides and the Isle of Skye. But the same amount of elevation would also suffice to unite us to the Continent from Denmark to Spain, as well as to push out our whole coast-line about fifty miles to the westward of Cape Clear. Beyond that distance the sea-bottom suddenly topples over from a general depth of a hundred fathoms to a depth of a thousand fathoms or more; which clearly shows that this line, curving round from Shetland to the Spanish shore of the Asturias, must mark an old and long-continued prehistoric land-barrier. In other words, the British Isles are situated on a comparatively shallow submarine bank, which spreads north, south, and east of them, but ends abruptly to the westward by a sudden drop of eight or nine hundred fathoms. If you were now to raise this bank a hundred fathoms in height, you would lift its whole area above the sea-level, save only in the two hollows already noted; but if you went on raising it for several hundred fathoms more, you would not materially alter the coast-line established by your first elevation. So we can hardly doubt that the hundred-fathom line really represents the old western boundary of Europe towards the Atlantic, because it coincides so nearly in depth with the elevation necessary to unite England and Ireland to one another, and to the Continent.
Only one element of our problem now remains to be solved; and that is the question — When did the subsidence take place which turned the dry land all round Britain into the beds of the English Channel, the German Ocean, and the Irish Sea? To this question I am deferentially inclined to give a somewhat different answer from that of most of our authorities. As a rule, it seems to be implied that the subsidence was a single act, spread indeed over a considerable length of time, but completed once for all, and never since renewed. It appears to me more probable, however, that the subsidence has been going on more or less ever since the age of the submerged forests, and that it still continues in places over the same area. Mr. Wallace has already pointed out that Ireland was probably separated from the mainland sooner than England, because it has fewer native mammals and hardly any reptiles or amphibians. The happy immunity from toads and serpents which is generally attributed to the pious exertions of St. Patrick, may perhaps rather be set down to the early isolation of Ireland from the mainland shortly after the end of the great ice age, and before all the members of the new European fauna had had time to spread equally over the more outlying portions of the yet undivided continent. But there are other indications of subsequent partial submergence elsewhere. Many facts lead me to the belief that the Bristol Channel was still a plain through which the Severn flowed quietly to the sea long after the final insulation of Ireland and the Hebrides. Tourists driving from Barmouth to Port Madoc have looked down from the picturesque escarpment of Harlech Castle upon a narrow belt of plain between the mountains and the sea, and have been told how the Lowland Hundred once stretched outward from this point across Cardigan Bay as far as Sarn Badrig or St. Patrick’s Causeway, a rocky reef which whitens the Channel into a long line of breakers in the middle distance. Welsh legends, immortalised by Peacock’s delicious satire, tell us how the Hundred was submerged by an inundation; and the tradition as to this subsidence is almost certainly correct. There is some ground for believing that the Isle of Wight was still united at ebb tide to the mainland of Hampshire by a sandy isthmus, when the Romans built their villas at Brading; and we know that even as late as the days when Hengest and Horsa launched their mythical long ships for the conquest of Kent, the Zuyder Zee was yet undoubtedly an inland lake, separated from the German Ocean by a long belt of land now almost entirely submerged, save in the solitary line of islands which preserves the outline of its northern shore. Nay, even in our own time, the southern part of Sweden is slowly sinking by inches beneath the level of the Baltic. Hence I am strongly inclined to suspect that the submergence of this western land was a work of time, and that no particular date can be assigned to it as a whole.
Now, when a continuous belt of lowland stretched round from Spain to Ireland and the Shetlands, we can easily understand that the warm type of south European plants would run northward along its western shore as far as the climatic conditions permitted. But the climate on all the west coast of northern Europe is exceptionally
mild and moist, through the agency of the Gulf Stream and the warm westerly breezes which blow across it. Hence it is not surprising that the Mediterranean heath, the strawberry tree, the pæony, the hairy spurge, and all the other southern plants which I have before scheduled, should have ranged all along the Atlantic shore of Europe, past the Pyrenees and the Asturias, up the bend a hundred and fifty miles west of the Land’s End, and so onward to Kerry and Connemara. Dr. James Geikie has recently shown good reasons for believing that the last glacial epoch was immediately succeeded by a short spell — say a thousand years or so — of very sunny and genial conditions in northern Europe; and while these favourable conditions lasted we can readily understand that the southern flora may even have extended along the sheltered belt beneath the mountain-ranges of Ireland and Scotland as far northward as Bute and Arran, where some few of its hardier representatives are actually still preserved. Meanwhile, the eastern level slope of what is now England, together with Holland and the intervening land which then filled up the basin of the German Ocean, must have had an inland continental climate, exposed to the full rigour of the north-east winds, and unmitigated by the warmth and moisture now diffused over it by the sea and its currents. In short, the condition of that great tableland must have been much like the condition of Central Russia at the present day, aggravated perhaps by an extra elevation to some hundreds of feet above its existing level. Here, then, the flora must have been of the central European and Scandinavian type; while west of the great central range of England, the trees and flowers must in the main have resembled those which we now find among the nooks of the Apennines and the Genoese Riviera.