Chapter IV: The Arctic Fauna (2)

Let us now look a little more closely at the history and the fauna of the Baltic and the adjoining lakes, in order to gain additional information as to the geographical changes which have had such lasting influence on the peninsula of Scandinavia. The Baltic is a shallow sea covering an area of 184,496 square miles, and its waters are decidedly brackish. The fauna is a poor one, being too salt for the purely freshwater species and not salt enough for the typical marine forms. The absence of some animals which we should expect to find there is one of the remarkable features about the Baltic, but, on the other hand, some species occur which are altogether strangers to the fauna. And these, moreover, are confined to the extreme northern end of the sea. I need only refer to the Arctic Seal (_Phoca annelata_), which is confined to the Gulf of Bothnia, and to the four-horned sting-fish (_Cottus quadricornis_, Fig. 14, p. 178), neither of which occur on the west coast of Scandinavia. But there are others which point in an equally unmistakable manner to the former existence of a marine connection between the Baltic and the southward prolongation of the Arctic Ocean--known as the White Sea. It is generally admitted now that such a union between these two seas, viz., the Baltic and the White Sea, occurred in recent geological times, but opinions differ as to the duration of this connection. I adhere to the view expressed by Murchison and others, that the boulder-clay is a marine deposit. I am also convinced that the Arctic Ocean, as I have already mentioned, transgressed over the lowlands of Northern Russia at about the time when the newer crags were being deposited on the east coast of England; that the same large sea also covered Northern Germany, Denmark, Holland, and the lowlands of Sweden, and laid down the lower continental boulder-clay which is spread over such vast tracts of land in those countries. I shall have occasion to refer to this again more fully in the next chapter; meanwhile, it should be remembered that this stage was followed by a partial retreat of the northern sea, though Scandinavia did not become joined to the Continent. The date of this retreat of the sea, represented in Fig. 13, corresponds probably to what is known as the inter-glacial phase of the Glacial period, and I think it must have been during this time that the Forest-Bed on the coast of Norfolk was laid down.[2]

None of the Siberian mammals apparently entered Scandinavia at the time when they invaded Central Europe and penetrated as far west as England and Western France. Nor did the great Oriental mammals, like the Mammoth and others, reach Scandinavia; and Professor Pohlig argued, on the strength of these facts, that the latter country was either for a very short time only free from ice, or that it had defective land-communication with the Continent during inter-glacial times. This seems to me scarcely to explain the facts of distribution and account satisfactorily for the absentees. Nor does it, of course, harmonise with the views that I have announced above. Professor Engler's remark (p. 131), that Scandinavia probably projected above the glacial sea as an island, is more in accordance with these views, though the term island is scarcely applicable to that country, since it was always, as I said, indirectly joined to the Continent (_vide_ Fig. 13, p. 170). The fauna of Scandinavia, both fossil and recent, points to a direct isolation of that country from the continent of Europe during a considerable period.

Another proof that Northern Russia and the lowlands of Sweden were covered by the sea comes to us from a study of the fauna of the relict lakes--the "Reliktenseen" of Leuckart. This name was first applied by Leuckart to lakes containing marine organisms, which are supposed to have been flooded by, or to have been in close communication with the sea at some former period, like the lakes Ladoga and Onega in Russia. His views have been worked out subsequently in greater detail by Loven and O. Peschel, who gave them their strong adherence. Many leading zoologists, such as Professor Sars and others, have since adopted them, and though discredited by Professor Credner, the theory still offers the best explanation for the origin of marine animals in freshwater lakes.

Professor Credner's contention, that marine mollusca are always absent from these relict lakes, seems at first sight a stumbling-block to the theory. But the explanation is really simple enough. It is to Dr. Sollas that we owe a very ingenious explanation of the origin of freshwater faunas. He showed that all freshwater organisms in their early stages of development are provided either with some process enabling them to attach themselves to a foreign object, or that they pass this period within the body of the parent. This is a provision of nature to prevent freshwater organisms from being floated out to sea, where they would perish, until they reach maturity and can cope with floods and currents. Had Professor Credner been aware of Dr. Sollas's views, no doubt he would have modified his criticisms, for, as most marine mollusca have free-swimming larvae, they would have little chance of becoming permanent residents of lakes. During their larval stage, marine molluscs are quite a prey to the currents of the sea. They have practically no swimming organs, and only move by lashing to and fro the tender cilia with which they are provided.

This disposes, therefore, of Professor Credner's main criticisms. As for the fauna of the relict lakes, we are now only concerned with those of Northern Russia, Finland, and Sweden. In the lakes Wetter and Wener in the latter country occurs the four-horned sting-fish (_Cottus quadricornis_, Fig. 14), which, as we have learned, also inhabits the northern part of the Baltic, and, as was suggested, migrated there at a time when the latter was connected with the White Sea. The principal food of this little fish consists in a marine Crustacean called _Idotea entomon_, an animal allied to our common woodlouse. This is a typical marine species, but it occurs also in the relict lakes of the countries mentioned above, as well as in the Baltic and the Caspian. Perhaps the best known form with a similar range is the Schizopod crustacean _Mysis relicta_[3] (Fig. 15), which is clearly a descendant of the Arctic marine _Mysis oculata_, of which it was formerly considered a mere variety. The two Amphipods _Gammaracanthus relictus_ and _Pontoporeia affinis_ and the Copepod _Limnocalanus macrurus_, are three additional well-known Arctic crustaceans whose range differs but little from those above-mentioned.[4]

These facts all go to prove that the sea formerly covered the lowlands of Sweden, Finland, and Northern Russia. The fauna of Scandinavia, as we have seen, indicates that during the greater part of the Glacial period the country was not directly connected with continental Europe as it is now. It seems that the barrier of separation probably consisted of a broad expanse of ocean on which floated numerous icebergs, which originated from the Scandinavian glaciers as they reached the sea. This was a cold sea, whilst Western Scandinavia was washed by the Gulf Stream (_vide_ Fig. 12, p. 156). We might look upon the boulder-clay which covers such vast tracts of country in Northern Germany, Russia, and Holland as deposits formed by this sea rather than the ground-moraine of a huge Scandinavian glacier. I shall refer to this subject again in the next chapter; meanwhile it may be remembered that the boulder-clay of Northern Europe exactly resembles in all important particulars the similar accumulations met with in the British Islands. They resemble one another also in the occasional occurrence of sea-shells, the frequent appearance of bedded deposits, and the often inexplicable course taken by boulders from their source of origin. There occurs often a singular mixture and an apparent crossing of the paths of boulders in the boulder-clay. Professor Bonney remarks (p. 280) that these are less difficult to explain on the hypothesis of distribution by floating ice than on that of transport by land-ice, because, in the former case, though the drift of winds and currents would be generally in one direction, both might be varied at particular seasons. So far as concerns the distribution and thickness of the glacial deposits, he says there is not much to choose between either hypothesis; but on that of land-ice it is extremely difficult to explain the intercalation of perfectly stratified sands and gravels and of boulder-clay, as well as the not infrequent signs of bedding in the latter. Two divisions are generally recognisable in the continental boulder-clay--a lower and an upper. An inter-glacial phase characterised by a less severe climate is assumed to have intervened between the deposition of the two. In Russia no such division can as a rule be made out, and sea-shells are either entirely absent or extremely scarce. It has been pointed out by Professor J. Geikie that the erratics--a name applied to boulders in boulder-clay--in the upper division have travelled in a different direction from those contained in the lower. Taking for granted that the boulder-clay is a marine deposit, this phenomenon seems to indicate that the current which prevailed during the early part of the Glacial period in this North European ocean was different from the prevailing current during the latter part. I have attempted to explain this circumstance by the supposition that during the early part of the Glacial period the Northern Sea had a connection with the Ponto-Caspian Sea--a sea formed by the junction of the Black Sea and the Caspian (Fig. 12, p. 156). There is geological evidence, as will be explained in the following chapter, that the area of these two seas was considerably larger in glacial times than it is now, and that they were joined across the valley of the Manytch. After the inter-glacial phase of the Glacial period, the North European Ocean became connected with the Atlantic Ocean across the north of England (Fig. 6, p. 126), the junction between the former and the Ponto-Caspian having meanwhile become dry land (Fig. 13, p. 170). A fresh current, now flowing westward, was set up in the North European Ocean, which accounts for the fact just cited that the erratics in the upper continental boulder-clay have travelled in a different direction from those in the lower. The boulder-clay laid down by the sea on the midland and northern counties of England, just as was the case with the similar deposit on the Continent, is generally accredited to the action of land-ice. It is by most geologists looked upon as the ground-moraine, partly of the huge Scandinavian glacier which is supposed to have impinged upon the English coast, partly of local British glaciers.

But renewed geological investigations on this point throw doubts upon these theories. Thus Mr. Harmer remarks in a recent contribution to glacial literature (p. 775), that "it is difficult to see how the Baltic glacier could have reached East Anglia, though ice-floes with Scandinavian boulders might easily have done so, while had the Norwegian ice filled the North Sea and overflowed the county of Norfolk, some evidence of its presence ought to be found in the glacial beds of Holland."

All the phenomena of distribution of the British fauna and flora are, as we have seen, much more easily explained by the supposition of a damp, temperate climate, such as might have been produced by the proximity of a cold sea on one side and of a warm one at the other, than by invoking an arctic climate with enormous glaciers. Most of the living animals and plants would have been exterminated under the latter conditions. Palaeontological evidence in Great Britain clearly indicates that southern species migrated first to these islands, that Arctic species were then driven south from their native lands,--probably owing insufficient food-supply and climatic changes in the north,--that finally eastern species invaded the country--all this without the annual temperature of Europe being apparently much affected. For we find in the British pleistocene deposits--and Mr. Lydekker draws particular attention to this remarkable fact--a curious intermingling of southern and northern mammals, which undoubtedly lived side by side. Everybody knows that northern and Arctic species can live perfectly well in a temperate climate, but that it is almost impossible to acclimatise southern animals in an Arctic or even temperate one. We have in this circumstance almost a proof, therefore, that the climate cannot have been very cold. Though a cold sea bathed the shores of Eastern England, and even eventually invaded a portion of Northern England, the warm ocean on the west must have effectually prevented any great lowering of temperature.

At the time when the North European Sea flooded a portion of England, Scandinavia was still connected with Scotland, and the latter with Ireland (Fig. 6, p. 126). There is no doubt that the food-supply in the Arctic Regions was decreasing with an increase of snowfall and with the gradual lowering of the land, which reduced also the habitable area. Arctic species therefore were driven south in search of fresh pastures. But it need not be supposed that anything like a vast destruction of the fauna of the Arctic Regions took place. Only fewer mammals were able to find food in a given space than heretofore. This southward migration may have commenced, in the case of plants and the invertebrates, at a much earlier time,--during the Miocene or Pliocene Epochs,--but it is doubtful whether the mammals and birds which we find in our pleistocene and recent deposits began to travel south much before the commencement of the Glacial period. The beginning of the Glacial period in England, I think, is indicated by the deposition of the Red Crag, though the latter is generally regarded as belonging to the pliocene series. Much of the northward migration from the British Islands of Lusitanian and other forms had then ceased, but we have in Scandinavia, just as in these islands, a southern relict fauna and flora, plants and animals which had wandered across what is now the German Ocean from Scotland to Scandinavia, and have never become extinct in that country to the present day. I need only mention the Red Deer, the Badger, and Slugs of the genus _Arion_.

Professor Blytt directs attention to some such southern relict species of plants now only found in the extreme south-west of Scandinavia, such as _Asplenium marinum_, _Hymenophyllum Wilsoni_, _Carex binervis_, _Scilla verna_, _Erica cinerea_, _Conopodium denudatum_, _Meum athamanticum_, and _Rosa involuta_ (p. 28).

The Arctic fauna and flora in Scandinavia--that is to say, the descendants of those species which migrated direct from Greenland and Spitsbergen, as we have seen, are numerous. They of course persisted throughout the Glacial period in the country, and are now in many localities being exterminated partly by change of climate, partly by a keen competition with more vigorous rivals which have come to Scandinavia from the east. It is a curious circumstance, as pointed out by Professor Blytt, that the Arctic plants in the Botanic Gardens at Christiania are able to stand almost any amount of sunshine, but are very liable to be injured by the frost, and have to be covered in the winter. A similar observation has been made in the case of the Alpine plants at Kew Gardens, which have to be wintered in frames, though their homes are either in the high Alps--among the everlasting snows--or in the intensely cold climate of Greenland. Many of the Scandinavian plants exhibit instances of discontinuous distribution, thus showing their ancient origin; and there is altogether nothing in the fauna and flora of that country which might lead us to believe that these were exterminated during the Glacial period and reintroduced subsequently. The climate during that period in Scandinavia was probably more equable and moister,--with a greater snowfall in winter and with less sun to melt the snow during summer,--so that the development of glaciers took more formidable dimensions, chiefly on the east side. The lowlands of Sweden were covered by the sea, whilst many of the valleys were choked with great glaciers, which cast off portions of ice as they reached the sea, just as the Greenland and other northern glaciers do (_vide_ p. 237). A country which at the present day probably somewhat resembles the former Scandinavia climatically is Tierra del Fuego, in the extreme south of South America. Though there is an abundant snowfall, so that glaciers reach the sea in many parts of the country, the flora has been described by travellers as luxuriant; and it appears that the fauna also is richer than might be expected from the cheerless climate.

Towards the latter part of the Glacial period the land-connection between Scandinavia, Spitsbergen, and Greenland broke down, and the waters of the Arctic and Atlantic Oceans joined. Whether it was at this time or later that the other land-connection between Scandinavia and Scotland collapsed is difficult to determine; but it is certain, I think, that Scotland was still united with Ireland even after these two great land-bridges ceased to exist.

SUMMARY OF CHAPTER IV.

The fauna of the Arctic Regions is much poorer than that of the other regions which are dealt with in this work. In some groups, such as Reptiles and Amphibia, there are no representatives at all, but no doubt a larger number of species existed there in earlier Tertiary times. At least we have fossil evidence that during the Miocene Epoch plants of many families flourished in Greenland of which no vestige is now left in the Polar area. Climatic conditions must therefore have changed, as in Europe. A gradual refrigeration took place, owing probably to the slow withdrawal of the current which supplied the Arctic Sea with warmth. Greenland and Europe were then connected, and the Arctic Ocean was separated from the Atlantic. This land-connection is supposed to have lain far north between Scandinavia, Spitsbergen, and Greenland, and must have persisted until towards the end of the Glacial period.

As the temperature decreased and the land-area available in the north diminished, the surplus population, consisting of animals and plants, and possibly also of human beings, moved southward. We have traces in Europe, and especially in the British Islands, of a very early migration from the north in the so-called American plants and in the freshwater sponges. The geographical distribution of some of the Arctic species of mammals is referred to in greater detail, to show how the relative age of their entry into Europe can be determined. Two forms of Reindeer, resembling the Barren-ground and Woodland varieties, have been met with in European deposits, but only the former occurs in Ireland and the south of France, whilst eastward the other becomes more common, and finally is the only one found. It is believed that the Barren-ground is the older form as far as Europe is concerned, and that it came to us with the Arctic migration, and that the other Reindeer reached Europe much later from Siberia, when Ireland had already become detached from England. The range of the Arctic Hare is equally instructive. It must have been a native of Europe since early glacial or pre-glacial times--before the common English Hare had made its appearance in Central Europe. Along with other Arctic forms, it entered Northern Europe directly from the Arctic Regions, by means of the former land-connection which joined, as I remarked, Lapland with Spitsbergen, Greenland, and North America. There need not have been a post-glacial connection between Europe and Greenland; the present flora of that country may have survived the Glacial period in the Arctic Regions, as has been maintained by some botanists and other authorities. Professor Forbes argued from the occurrence of the same species of shore mollusca on the coast of Finmark and Greenland that these two countries were not long ago joined, so that a slow migration from west to east along an ancient coast-line could have taken place. That such a migration actually occurred is further made probable, judging from the presence of American mollusca in the Crag deposits on the east coast of England. These came into the North Sea in the first place direct from the Arctic Ocean at a time when the two oceans freely communicated with one another across the lowlands of Northern Russia, Northern Germany, and Holland. Arctic shells are also found below the boulder-clay on the Baltic coast, and a free communication such as indicated is generally held to have taken place at no very distant date. The so-called "relict species"--marine animals left in freshwater lakes in districts formerly covered by this sea--lend some support to this view. But the view that the continental boulder-clay is a marine deposit is not now held except by a few, though I here bring it forward again, as it seems to me to fit in so much better with the known facts of distribution. The sea just referred to probably existed throughout the greater part of the Glacial period; and icebergs, which originated from the Scandinavian glaciers, would have brought detritus and boulders to the lowlands. Scandinavia was then connected with Scotland, and England with France.

FOOTNOTES:

[1] A very interesting piece of information has been given us, recently, by Mr. Barrett-Hamilton on the Arctic Fox of Spitsbergen. In comparing the skulls of Spitsbergen Foxes with those of Europe, he found that the former are much smaller, and represent a distinct race or sub-species. This small race he believes to be confined to Greenland, Iceland, Spitsbergen, and Novaya Zemlya, whilst the larger one occurs in Europe, Asia, and on the Commander Islands. This fact favours the view which I have advocated in Chapter V., that the Arctic Fox in Europe is a Siberian migrant, and did not come from the north with the Reindeer and Arctic Hare.

[2] I have already expressed this view on p. 120.

[3] The occurrence of this species in Lough Neagh in Ireland, pointing to a connection between the Irish Sea and the Baltic, will be referred to later on; as also that of two allied forms in the Caspian Sea.

[4] For additional species with a similar range, _vide_ Nordquist.