1902 Encyclopedia > Baltic Sea

Baltic Sea




BALTIC SEA. The name by which this inland sea is commonly designated is first found in the 11th century, in the work of Adam of Bremen, entitled Chorographia Scandi-

Sketch Map of Baltic Sea,

navica. The derivation of the word is uncertain. It seems probable that, whatever may be the etymology of the name Baltic, that of the Great and Little Belts is the same. The Swedes, Danes, and Germans call it the Ostsee or East Sea.

The Baltic is enclosed by Sweden, Russia, the German empire, and Denmark; and it communicates with the North Sea, by the winding channel which lies between the southern part of the Scandinavian peninsula and the northern peninsula of Schleswig and Jutland. The first part of this channel is in great measure blocked by the islands of Zealand and Fiinen, so as to form the three narrow passages which are known as the Sound (between Sweden and Zealand), the Great Belt (between Zealand and Fiinen), and the Little Belt (between Fiinen and Jutland). Each of these forms a distinct communication between the Baltic and the Cattegat, which is the open portion of the channel lying between the coast of Sweden and the eastern side of Jutland ; while the Cattegat opens freely into the Skager Rack, which is the continuation of same open channel, between the southern end of Norway and the north-west coast of Jutland, into the North Sea.

The length of the Baltic Sea, from Swinemünde in the S. to Tornea in the N., is nearly 900 miles; and its greatest width, between Karlscrona and Memel, exceeds 200 miles. Its whole area, including the Gulfs of Bothnia and Finland, is about 160,000 geographical square miles. It runs first in an easterly direction as far as Memel, a distance of 300 miles, and then northwards as far as lat. 59° 21' N., a distance of 350 miles, at which point it separates into two great gulfs. One of these, the Gulf of Finland, runs nearly due E.; the other, the Gulf of Bothnia, almost N.1 The Gulf of Bothnia is 400 miles in length, with an extreme breadth of 120 miles, but where narrowest it does not exceed 40 miles. The archipelago of Aland lies at its entrance. The Gulf of Finland is 280 miles in length, with a mean breadth of 60 or 70 miles.

The depth of the Baltic rarely exceeds 100 fathoms— being greatest between the island of Bornholm and the coast of Sweden, where it reaches 115 fathoms, and least in the neighbourhood of the mouths of large rivers, which bring down a great quantity of earthy matter, especially in the spring, so that in many parts the bottom is being so rapidly raised by its deposit that the mouths of rivers formerly navigable are now inaccessible. This is especially the case in the northern part of the Gulf of Bothnia, above Quarken, where several tracts are now. dry land which were once water ; and also in the neighbourhood of Tornea, where meadows now take the place of waters which were traversed in boats by the French Academicians, when they were measuring an arc of the meridian. Along the southern coast the shallowness of the harbours is a great obstacle to navigation, especially since they are closed by ice for nearly one-third of the year. On the western side it is not more than 15 fathoms deep; and, in general it is only from 8 to 10 fathoms. On the S. it nowhere exceeds 50 fathoms. The Gulf of Finland suddenly shallows from 50 or 60 fathoms to 5, or even less. The average depth of the Gulf of Bothnia is not greater than that of the rest of the sea. Numerous rocky islands and reefs, many of them level * with the water, render the navigation of this sea extremely dangerous.

The shore of the Baltic is generally low. Along the southern coast it is for the most part sandy,—with sandbanks outside, and sand-hills and plains inland. Where streams come down, there are often fresh-water lakes termed haff*, which are separated from the sea by narrow spits called nehrungi. Two of these haff* are of great extent; one of them, termed the Frische Haff, lies between Danzig and Königsberg, which last town is situated on the part of it most remote from the sea; the other, termed the Kurische Haff, lies between Königsberg and Memel, the latter town being situated on the channel connecting the haff with the sea. Near the entrance to the Gulf of Finland the coast becomes rocky, and continues to be so for the most part around the gulfs both of Finland and Bothnia, except towards the head of each; the rocks, however, are never high The shores of the southern part of the Swedish peninsula are mostly high, but not rocky; at Stockholm, however, there is an archipelago of rocky islands, on some of which the town is partly built.

Drainage Area.—The Baltic may be considered as the estuary of a great number of rivers, none of them individually of great size, but collectively draining a very large area, which is estimated at about 717,000 square miles, or nearly one-fifth of the entire area of Europe. This great drainage area is remarkable for the small proportion of its boundary that is formed by mountains or high table-lands,—its greater part consisting of land of no considerable elevation, which slopes down very gradually to its coast-line, and of which a large proportion is covered by lakes. This is especially the character of the drainage area of the Neva, whose waters are immediately derived from the large shallow Lake Ladoga, which receives the contributions of numerous other lakes, Onega being the largest, though Lake Saima in Finland, with its irregular prolongations, is scarcely less extensive. The entire surface drained by the Neva is esti-mated at about 100,000 square miles, or nearly twenty times that of the drainage area of the Thames. Through Lake Onega, the Neva is connected with the Dwina and the Volga by canals, through which small vessels can pass from the Baltic into either the White Sea or the Caspian. The Duna or South Dwina, which discharges itself into the Gulf of Riga, is another important river, draining an area of about 35,000 miles in West Russia, and having a length of 520 miles, of which 405 miles are navigable. The drainage area of the Niemen, which enters the Baltic at Memel, is conterminous with that of the Duna, and is of about the same extent, this river is navigable for more than 400 miles from its outlet, and communicates with the Dnieper by a canal through which vessels can pass from the Baltic to the Black Sea. The Vistula, which receives the waters of the whole area of Russian and Prussian Poland, flowing past Warsaw into the Baltic at Dantzig, is a very large and important river, having a length of 520 miles, of which 430 are navigable, and a drainage area of 72,000 square miles. And the Oder, rising in the hill districts of Silesia, drains the extensive level areas of Brandenberg and Pomerania, and discharges into an estuary, that may be said to begin from Stettin, the water drawn from an area of 45,000 square miles. Numerous rivers discharge themselves into the Gulf of Bothnia, bringing down water from the mountain ranges of Sweden and Norway ; but their course is comparatively short and direct, with few tributaries, so that, individually, they do not attain any great size. The drainage of the more level southern portion of Sweden is for the most part collected by the great lakes Wener, Wetter, and Malar, of which the first pours its water into the North Sea, and the others into the Baltic. By means of a canal joining Lakes Wener and Wetter vessels can pass directly from the Cattegat into the Baltic.

Climate.—It is not only, however, the extent of it* drainage area, but the large proportion borne by the rain and snow which fall upon that area to the amount dissipated by evaporation from its surface, that goes to swell the aggre-gate of fresh water poured into the basin of the Baltic; for there is probably no inhabited region of the whole globe over which so large a quantity of snow falls, in proportion to its area, as it does in the countries round this basin. They receive, direct from the Atlantic, a vast amount of moisture brought by its west and south-west winds ; and even the winds which have already passed over the low plains of Jutland and Northern Germany will have parted with little of their moisture before reaching the Baltic provinces of Russia. When these vapour-laden west and south-west winds meet the cold dry east and north-east winds of Siberia, their moisture is precipitated, in summer as rain, and in winter as snow; and owing to the prevalence of a low atmospheric temperature through a large part of the year, the proportion lost by evaporation is extremely small as compared with what passes off from other inland seas. The large excess of the amount of fresh water discharged into the basin, over that which passes off by evapo-ration from its surface, is indicated by its low salinity, which, however, varies considerably in its different parts and at different seasons of the year. The temperature of the Baltic is remarkable for its range, which is rather that of a terrestrial than of a marine area—this being doubtless owing in great degree to the fact that its shallowness and the low salinity of its water allow a large part of its surface to be frozen durmg the winter. Nearly the whole of the Gulf of Bothnia, with the land enclosing it on both sides, lies between the January isotherms of 10° and 20°—the former crossing it near its head, and the latter near its junction with the Baltic proper ; and the whole of the Baltic proper, with the land enclosing it on the east, south, and west, lies between the January isotherms of 20° and SO*. On the other hand, the July isotherm of 60°, which crosses England near the parallel of 54°, passes across the Gulf of Bothnia near the Walgrund Islands, almost 9° further north ; and the whole of the Baltic proper, with the Gulf of Finland and the southern part of the Gulf of Bothnia, lies between the July isotherms of 60° and 66°. Thus the range between the mean summer and mean winter temperatures, which is only about 20° in the British Islands, is about 40° over the Baltic area. The mean annual temperature of the Gulf of Bothnia ranges between 30° at its northern extremity and 40° at its southern, while that of the Baltic ranges from 40° at its northern boundary to about 46° at its southern.

Formation and Transportation of Ice.—The greater part of the Gulfs of Bothnia and Finland is usually frozen over during the winter, the formation of ice beginning at the head and extending downwards. Masses of ice, conveyed by the currents into the Baltic proper, freeze together as the winter advances, and form vast fields, generally extending on the east side as far south as the islands of Dago and Oesel, and on the west to the south of Stockholm. It happens sometimes, though rarely, that large portions of the Baltic proper are continuously frozen over; but naviga-tion is usually interrupted by the blocking up of its bays and harbours with ice, from the latter part of December to the beginning of April The freezing of the Gulfs of Bothnia «nd Finland begins earlier and ends later.





The curious phenomenon of the formation of bottom-ice, and its rise to the surface, is more frequently seen in the Baltic and the Gattegat than in the open ocean,—chiefly, it seems probable, on account of the shallowness of these seas. It has been particularly observed by Prof. Nilsson in the Gattegat, off Kullen Point, near the southern extremity of Sweden ; but according to Chydenius it is very common in various parts of the Baltic, having been especially noticed by the fishermen off the Aland Islands. In calm winter weather, water of from 4 to 8 feet deep is often covered in a very short time with small plates of ice, mostly circular in form, varying in diameter from 1 to _ inches, and having a uniform thickness which never exceeds two lines. These plates can be seen coming up from below, rising edgeways towards the surface, often with such force as to lift them-selves three or four inches out of the water. When they come up in great numbers they are often pded one upon another, and are then usually soon broken, by the action either of waves or of currents, into small pieces, which unite again by regelation so as to form irregular cakes of ice ; and these, as soon as the water becomes tolerably still, cohere into a continuous rough sheet. But it sometimes happens that if the plates come up more sparsely, and the weather is very still and cold, they remain unbroken, and the diameter of each increases, sometimes to two feet or even more. When the fishermen notice these ice-plates coming up from below in large quantities, they at once make for land, as they know that they might otherwise be soon completely ice-bound. The same thing appears to happen in polar seas in the shallow water near land. Chydenius, who was a member of the Swedish Spitzbergen expedition in 1857, states that on one occasion the surface of the sea, which was previously quite clear of ice, became so covered in the course of half an hour, that it was with difficulty that a boat could be forced through it; and this although the temperature of the air during the day had not been lower than 4° C, and no wind or stream had brought the ice together.

It does not seem very clear in what way this formation of bottom-ice is to be accounted for. Bottom-ice has often been noticed in fresh-water lakes and streams; and large plates have been seen to rise to the surface, sometimes with force enough to bring up stones of considerable size,—in one instance a heavy iron chain. In these cases it would seem that the motion-of the bottom-water over roughened surfaces contributes to its congelation. And in the shallow water near the sea-shore, stones and sea-weeds may be seen covered with ice, like the hoar-frost on trees, before any ice forms on the surface. It is to be remembered that sea-water increases in density down to its freezing point, so that the water cooled at the surface will always go down, the deepest stratum being thus the coldest. And thus, although no lower temperature can be carried down by the water than that to which it has been subjected at the surface, the water that does not freeze at (say) - 2°'5 C. when lying upon water, changes into ice when it comes in con-tact with the irregular solid bottom, perhaps on account of the more ready dissipation, under the latter circum-stances, of the heat set free in the act of congelation.

When ice forms over the shallow bottoms which border parts of the Gulfs of Bothnia and Finland, large blocks of stone are frequently frozen into it; and these, being lifted when the water rises in the early summer, are often transported by currents to considerable distances, finally subsid-ing again to the bottom when the ice melts. In this manner a deposit of rocky fragments, some of them 6 or 8 feet across, is being formed at the bottom of the Baltic outlets; as is known from the fact, that sunken ships which have been visited by divers in the Sound and in Copenhagen roads have been found covered with such blocks within no very long period. It not unfrequently happens, moreover, that sheets of ice with included boulders are driven up on the coast during storms, and are thw carried some way inland, being sometimes packed to a height of even 50 feet. A case was described by Von Baer in which a block of granite, whose weight was estimated at between 400 and 500 tons, was thus carried by the ice during the winters of 1837-8; and Forchhammer mentions that the Sound being suddenly frozen over during an intense frost in February 1844, sheets of ice driven by a storm were heaped upon the shore of the bay of Taarbeijk, and frozen into one mass so as to form a mound more than 16 feet high, which threw down the walls of several houses, and left behind it ridges of sand and pebbles when it thawed. It is apparently, moreover, by similar agencies, that th? fringe of rocky islands of all dimensions called the Skar, which lies at a little distance from the shore of many parts of the Baltic, is being gradually modified. Boats and small vessels can sail in smooth water within this skar, even when the sea outside is strongly agitated ; but the navigation is intricate, and the danger from sunken rocks to those not thoroughly acquainted with it is very con-siderable. The diminution which has Tjeen noticed from time to time in the depth of the channels, and the appear-ance above water of what were formerly regarded as sunken rocks or reefs, have been regarded as concurring with other evidence to prove that a general rise of land is now going on over this area. But it seems probable, from what has now been stated, that the increase of height and dimensions which has been observed in the reefs and inlets of the »kar during the last half century, may be adequately accounted for by the action of ice, which has piled up (generally on a basis of fixed rock) accumulations of trans-ported debris.

Rise of Land around the Baltic.—Early in the last century the Swedish physicist Celsius (to whom we owe the invention of the centigrade scale) formed the opinion that the waters both of the Baltic and of the North Sea were gradually subsiding; and this opinion, though controverted by other authorities, was embraced by Linnaeus. It is now clear that many of the facts by which it was supported are explicable by the transporting agency of rivers and of ice, as already explained; and it was pointed out by Playfair in 1802, that even admitting the proofs on which Celsius relied, they would rather show that the land is rising, than that the water is receding. During the present century a great deal of attention has been given to this question, on account of its geological interest, by many very able observers ; and the results may be briefly summarised as follows :—(1.) An elevation of the whole of Norway, from the North Cape to the Naze, has taken place within a comparatively recent period,—as is evidenced by the numbers of raised beaches containing existing shells, which are found at different points along the western coast, fre-quently at a height of 200 feet above the present sea-level, and in some spots at a height of more than 600 feet. As these beaches, where one lies above another, are not always parallel, it appears that the elevatory action did not take place equally over the whole area; and the movements were probably intermittent, with long pauses between. (2.) At various points along the coast of the Baltic and the Gulf of Bothnia, alike in Sweden and in Finland, similar collections of shells have been found, belonging to species now in-habiting the basin, and characterised by the peculiar fades to be presently noticed as distinguishing its molluscan fauna from that of the ocean. Such deposits have been found very far inland, and at a height of 230 feet above the sea. Bence it appears that before this upheaval took place, the Baltic must have been separated, as now, from the North Sea by the mountain ridge of Norway, although it ex-tended over a considerably larger area of what is at present low-lying land. (3.) Notwithstanding the numerous ob-servations which have been made with a view to ascertain whether any change of level is now going on, the question roust be regarded as still undetermined. Little reliance can be placed on occasional comparisons of the height of marks made upon rocks above the sea-level, since, although there are no tides, the height of the water in the basin is subject to considerable variations, from causes to be presently explained. (4.) There is a good deal of evidence, on the other hand, that, towards the southern extremity of Sweden, there has been a depression of the land since the historic period. In this portion, known as Scania, no elevated beds of recent marine shells have been met with ; in its seaport towns there are streets now at or even below the level of the water, which must have been above it when first built; and a large stone whose distance from the sea was measured by Linnaeus, in 1749, was found 100 feet nearer the water's edge when its distance was again measured in 1836. Near Stockholm, again, a fishing-hut, with remains of boats of very antique form and construction, was found, in 1819, at a depth of 60 feet, covered over with gravel and shell-marl; and it was considered by Sir C. Lyell to be impossible to explain the position of this hut without imagining first a subsidence to the depth of more than 60 feet, and then a re-elevation. On the whole, it appears clear that oscillations of level, not uniform either in direction or in degree, have taken place in various parts of the Scandinavian peninsula within a recent period, whilst in regard to the continuance of any such changes at the present time we have no certain knowledge, though it is considered probable by many of the most distinguished savans both of Sweden and Norway.

Movements of Water in the Baltic.—There is scarcely any tidal movement in the Baltic; for though there are sensible tides in the Skager Back, these begin to diminish in the Cattegat, and are very trifling in the Sound and Belts, averaging only about a foot at Copenhagen. There is usually a general movement of the upper waters of the Baltic towards the three channels which form its outlet, and a considerable flow of water through them. The large volume of water discharged by the rivers that empty themselves into the upper end of that gulf forms a southward current, which becomes very rapid where it narrows at Quarken (being partly blocked also by the Walgrund Islands), and again where it is obstructed by the Aland Islands, as it enters the Baltic proper. In that part of the basin the current is liable to considerable modifica-tion from prevalent winds; but it is usually very perceptible in the spring and early part of the summer, when the snows are melting. On the other hand, when an unusual con-tinuance of north-west wind concurs with high spring-tides to drive the water of the North Sea into the outlet of the Baltic, a large body of water flows back into its basin, producing a reverse current, which is felt as far as Danzig.





There are also considerable variations in the height of the water, that seem for the most part referrible to three different conditions, which may operate separately or in combination, viz., (1), the seasonal increase and decrease of the amount of water brought down by rivers; (2), the banking-up of the outflow by opposing winds; and (3), variations in atmospheric pressure.

(1.) During the winter months the quantity of fresh water poured into the Baltic by the rivers which dischargb themselves into it is greatly reduced by the freezing of their sources; and this is, of course, especially the case with those that empty themselves into the Gulf of Bothnia. Hence the general level of the surface is at its lowest at this season. With the melting of the snow in spring and early summer, however, there is an enormous increase in the quantity of fresh water poured into the basin, and the level of its surface then rises. There is always, of course, a tendency to equalisation of the level of the Baltic with that of the sea outside, by outflow or inflow currents through its three channels of communication; but the narrowness of these prevents that equalisation from being immediate, and it is often interfered with by winds. (2.) The influence of winds in banking up the water at the outlets, and even in reversing the usual currents, i* very decided, as has been especially shown by the recent researches of Dr Meyer of Kiel.* The strongest and most constant surface-outflow is seen during the autumn and winter months, when there is little or no elevation of level, but when the prevalent direction of the wind is such as to drive the Baltic water towards and through the straits. When, on the other hand, the winds prevalent in the North Sea tend to drive its water into the straits, their usual out-current may be reversed ; and this most frequently happen o during the spring and summer months, although the excess water to be discharged is then at its greatest. It sometimes happens, especially about the autumnal equinox, that a N.W. gale concurs with a high tide in the Skager Rack to drive its water towards the Baltic, causing it to overflow the lower portions of some of the Danish islands. If, then, a southerly wind should carry this water onwards into the Gulf of Finland, the check which it gives to the downflow of the Neva produces disastrous inundations at St Peters-burg. (3.) The influence of atmospheric pressure upon the height of the water in the Baltic is very remarkable. It had long been noticed that its level occasionally rises even aa much as 3 feet without any apparent cause, and maintains itself at that height, sometimes only for a few days, but occasionally for several weeks together, and this at all seasons. Schulten, having observed that such elevations of level are preceded by a fall of the barometer, and that when the barometer rises again the water subsides, was led to recognise the dependence of these changes upon converse changes in atmospheric pressure; and this reference was confirmed by observation of the constant proportion borne by one to the other. A similar con-sequence of variation in atmospheric pressure has been observed in the Mediterranean (see MEDITERRANEAN) ; and it has also been noticed in England as a disturbing ele-ment in modifying the height of the tides.

Salinity of Baltic Water.—As might be expected from what has been already stated, the proportion of salt in the water of the Baltic is very much below that of oceanic water, and varies greatly at different seasons. In the Gulf of Bothnia, at the time the river-flow is greatest, the surface water is often so little salt as to be quite drinkable, its sp. gr. having been found as low as 1 o004. But it is said to contain at Christmas six times as much salt as at midsummer, showing that when the river supply is at its lowest, its place is taken by a reflux of salt water from the outside ocean. In the Baltic proper there is a very decided difference in salinity between the upper and the lower stratum; the less saline water of the surface flowing towards the outlet over the more saline water beneath, just as the fresh-water current of a great river runs out to sea, even far beyond the sight of land. Thus the proportion of salt in 1000 parts of a sample of *Mr/oce-water taken near Stockholm being 5-919, that of bottom-water, brought up from 120 fathoms, was 7-182 ; and in like manner the proportion of salt in sur/ace-water at the entrance of the Gulf of Finland being 3*552, that of 6o#ojra-water at 30 fathoms depth was 4-921,—the proportion of salt in North Sea water averaging 32-823 parts in 1000. Nearer the outlet the proportion of salt is greater alike in surface and in bottom-water. From the careful and systematic observations of Dr Meyer (op. cit.), it appears that the sp. gr. of the surface-stratum at Kiel ranges between about 1-0082 in summer and 1*0142 in winter, the latter showing somewhat above half the quantity of salt contained in ordinary sea-water. But if the direction of the prevalent winds during the autumn be such as to maintain a strong surface out-current, and consequently (as will presently appear) a very strong inward under-current, as happens in some years, the maximum of salinity will present itself at that season. The sp. gr. of the deeper stratum ranges at Kiel from 1-0145 to 10190; at Helsingor on the Sound from 1-0190 to 1-0220 ; and at Korsor on the Great Belt from 1-0180 to 1*0243; thus showing it to be principally composed of North Sea water, whose sp. gT. may be taken as 1 0264.

Currents in the Baltic Straits.—The results of observation of the movements of the upper and under strata of water in the Baltic Straits, strongly confirm the doctrine else-where enunciated (see ATLANTIC) in regard to the potency at slight differences of downward pressure in the production of under-currents. The prevalent movement of the upper stratum in the Baltic Straits is outward ; and this concurs with the low salinity of Baltic water to indicate that it is partly an overflow current, produced by the excess of river supply over loss by evaporation, which tends to raise its leveL But even when this outward surface-current is strong, there is usually an inward under-current of North Sea water, carrying back into the basin of the Baltic a large proportion of the salt which would otherwise be lost to it; and the existence of this under-current, which has been abundantly established by experimental inquiries, as well as by the observations of divers, is exactly what theory would lead us to predict. For if two columns of water of the same height, but differing in specific gravity, be made to communicate with each other alike at the surface and at the bottom, the lower part of the heavier column, having a greater lateral pressure, will flow towards the fighter, thus tending to produce an elevation of level in the latter, which will rectify itself by a surface-flow in the opposite direction; and thus a vertical circulation will be maintained, as long as the causes which maintain the difference of salinity remain in operation. Now, as the salinity in the oceanic column may be regarded as practically constant, whilst the salinity of the Baltic column, though not uniform, is kept down by the influx of river-water to a much lower degree, this difference will always exist to a greater or less amount. "When, however, the height of the Baltic column is so much raised—either by the excess of its fresh-water supply, or by the reversal of the surface-current by the agency of wind—that the downward pressure of its less saline water exceeds that of the more saline water of the North Sea column, the under-current will be brought to a stand, or its direction will be reversed. Thus it is that when the outward movement of the upper stratum depends rather upon the prevalent winds (as is usually the case during autumn and winter) than upon the elevation of its level within the basin, the inward under-current which supplies its place is strongest and most constant. And it is by this means, much more than by the occasional reversal of the surface-current, that salt is carried back into the Baltic,—as is proved by the close correspondence shown by Dr Meyer's observations to exist between the predominance of the inward under-current and the elevation of the sp. gr. of the surface-water of the Baltic. On the other hand, it is during the spring and summer months, when the outward movement of the upper stratum is rather an overflow-current, and the salinity of the surface-water is the lowest, that the under-current sets less strongly and less constantly inward.

Zoology.—The fauna of the Baltic may be regarded as that of a large estuary, having a narrow communication with the sea,—its marine inhabitants being such as can adapt themselves to considerable variations in the salinity of its water. Whales rarely enter the Baltic; but porpoises fre-quent the neighbourhood of the Danish islands. Seals are obtained in considerable numbers at the breaking up of the ice around Gottland and the Aland Isles. The salmon is among the most abundant fishes of the Baltic proper, ascending its rivers from April to June; and salmon-trout are caught in some of its bays. The portion of the Baltic in the neighbourhood of the Danish islands is frequented by various species of Gadicke, which do not range further east. In the 14th and 15th centuries there was a consider-able herring-fishery within the Sound and along the coast of Scania (the southern portion of Sweden); but this fish seems to have latterly quite deserted the Baltic, and rarely shows itself even in the Cattegat. On the eastern coast of Sweden, on the other hand, and in the Gulf of Bothnia, a fish called the stromling, which is nearly allied to the herring, being chiefly distinguished by its small size, is caught in great numbers, and is dried and salted for distant markets. The molluscan fauna of the Baltic is chiefly made up of common shells of our own shores,—such as Cardium, Mytilus, and Littorina, which can bear an admixture of fresh water, together with several proper fresh-water shells, such as Paludma, Neritina, and Lymnasa; the marine types, however, being remarkable for their very small size, which is often not above one-third of their usual dimensions. There is an entire absence, except in the neighbourhood of the straits, of such essentially marine types as Buccinum, Ottrea, Pecten, Patella, and Balanus. It is interesting to remark that the Danish Kjbkkenmddding contain abundance of oysters, and also of full-sized cockles, mussels, and periwinkles; from which it may be inferred that even within the human period the outside ocean had freer access to the basin of the Baltic than it has now,— probably through what is now the peninsula of Jutland, which seems at no remote period to have been an archipelago. (w. B. O.)


Footnotes

The shells found in the raised beach at Uddevalla by Mr J. Gwyn Jeffreys in 1862, were characterised by him as glacial; but they have been shown to be specifically identical with mollusca now living at Spitsbergen ; and it is probable that when the water was deeper than at present along the coast of Norway, these would have ranged south-wards along the cold bottom, as they do even now to a certain extent.

2 UntersucKungm liber PhysikaUsche VerhJiltntsst des Vfest&ohm ThtUet der Ostset.




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