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BALTIC — BALTIMORE still prevailing at the time, this seems an unnecessary assumption. deep basins is intermittent, probably with a long period of flux In the next stage of its history the Baltic is transformed by further and reflux. The circulation in the channels connecting the Baltic proper elevation into a vast freshwater lake, the Aiicylus lake of De Geer (named from the remains of the mollusc Ancylus fluviatilis), which with the North Sea is of a complex character. It is necessary in first place to distinguish clearly between outflowing and inis supposed to have covered an area of about 5/0,000 scp km. the (220,000 miles), including the whole of the present Baltic area and flowing waters, and in practice this is easily done, because the outflowing water always contains less than 30 pro mille of salt, and a large part of Finland, with Lake Ladoga. Then followed a subsidence, which not only re-established communication through the inflowing water more than 32 pro mille. Since the Baltic the Danish channels, but allowed the Baltic to become sufficiently receives much more water by rainfall, discharge of rivers, etc., than loses by evaporation, a surplus must be got rid of by an out.salt for such forms as Cardium edule and Littorina littorea. At it current which may be named the “Baltic Stream.” The this time the Gulf of Bothnia must have suffered greater depression flowing general laws may be laid down with regard to this :— than the Baltic proper, for the deposits of that epoch show a thick- following 1. That the Baltic Stream must be a surface current, because it ness of 100 metres (328 feet) near Hernbsand, but of only 25 metres originates from a redundancy of fresh water. (82 feet) in the neighbourhood of Gothland. After this period of 2. That, on account of the earth’s rotation, the main part subsidence the process of elevation set in which gave the Baltic its the Baltic Stream must keep close to the coast of the Scanpresent form and physical condition, and appears to be still in of progress. Dr Sieger has traced a series of isobasic lines, or lines dinavian peninsula. 3. That it must be a periodic stream, because the discharge of of equal rate of elevation, for portions of Sweden and Finland; rivers into the Baltic varies with the season of the year. In these indicate that the movement is now almost nil along the the and summer the water from the Baltic is sufficiently axial lines of the Baltic and the Gulf of Finland, but increases spring to inundate the whole surface of the Kattegat and in amplitude northwards to the Gulf of Bothnia and in the abundant Skagerrak, but in winter the sources of the Baltic current are for direction of the main ridge of the massif of southern Sweden. At Stockholm the rate of elevation is approximately 0'47 m. ( = 1-54 the most part dried up by the freezing of the land water. All the waters which enter the Skagerrak or Kattegat as underfeet) in a century. can be found at the surface of the North Sea (see North The drainage area of the Baltic is relatively large. According to currents They may be divided according to their origin and salinity the measurements of Murray it extends to 461,450 square sea miles Sea). follows:— (= 611,700 square English miles). The largest river basin included as {a) Ocean water of 35 pro mille salinity or more. in it is that of the Neva in the east, and next in size come the (b) North Sea water, the predominant water in the North Sea Vistula and the Oder in the south. The narrow parallel troughs, area, of 34 to 35 pro mille salinity. at right angles to the coast, which form the drainage system of (c) Bank water, 32 to 34 pro mille, which forms a broad Sweden and western Finland, are a remarkable feature. covering the coast banks of Holland, Germany, Denmark, The coast of the Baltic is rocky only in the island-studded edging Norway. -it region at the head of the Baltic basin proper—a submerged lake- andThe water stratum in the Skagerrak is certainly ol district—and the littoral generally is a typical morainic land, the oceanic deepest
- it has been found to suffer changes of long period,
work of the last great Baltic glacier. The southern margin of the and it isorigin not always composed of -water derived from the Baltic is of peculiar interest. From Schleswig eastwards to Liibeck same partprobably or the same depth of the North Atlantic ; this water is, Bay the coast is pierced by a number of narrow openings or Fohrde, as a rule, deficient in oxygen. The “North Sea’’water, of 34-35 the result of encroachment of the sea caused by subsidence. East pro mille salinity, does appear at the surface in the Skagerrak, of Liibeck, as far as the mouth of the Oder, these give place to except as a strip alongnotpart of the coast of Jutland, but it is Sodden, ramified openings studded with islands: the structure always found as an undercurrent overlying the oceanic water. It here resembles that of Scania in southern Sweden, a region once enters into all the deep coast channels, and into the Christiania joined to both Denmark and Pomerania by an isthmus which was fjord, but it is not always found in the channels of the severed by tectonic movements. Beyond the Oder the coast-line is Kattegat. The principal time of inflow ofdeep North Sea water is unbroken as far as the Gulf of Danzig. It is then cut into by the during spring and summer. The bank-water of to 34 pro mille estuaries of the Vistula, the Pregel, and the Memel. Here the salinity is found all along the continental coast 32 of the North Sea westerly winds have full play, and the coast is rimmed by a con- and North Atlantic, and it may therefore enter tinuous line of dunes, which cut off the two great lagoons of the either from the North Sea or from the north alongthetheSkagerrak coast of Frisches Haff and Kurisches Eaffbj sand-spits or Nchrunge. Levellings from Swinemiinde show that the mean level of the Norway. It is probable indeed that an influx of this water occurs both directions—in August and September from the s°utb, surface of the Baltic at that point is 0-093 metres (=-305 feet) from in the late winter and early spring from the north. The below the surface of the North Sea at Amsterdam, and 0-066 and changes in the distribution of the bank-waters m metres (=-216 feet) below its level at Ostend. A line of levels seasonal parts of the coast are too complex to be briefly explained; from Swinemiinde through Eger to the Adriatic showed the mean different relations to the times of occurrence of various fisheries^ of the level of the surface of the Baltic to be 0-499 metres (1'6 feet) above their present many remarkable features, which have been investithat of the Adriatic Sea. The mean level of the surface of the region in recent years by the Sivedish Commission.^ Baltic rises about 0"5 metres (1"6 feet) from the coast of Holstein gated On the wTest and south coasts of Sweden, and in the Skagerrak to Memel, probably as a result of the prevailing westerly winds ; south-east of Norway, navigation is interfered with by ice only m this mean difference is exceeded with strong westerly winds, and severe winters, then the ice is usually drifting, compact seadisappears or is reversed with easterly winds. The waves of the ice being very and rare. Between Stockholm and W isby navigation Baltic are usually short and irregular, often dangerous to naviga- usually ceases at the end of December and begins again about tion. Destructive waves, probably caused by distant earthquakes, 10th April. During very winters the Aland Sea is covered called Seebdren (c/. English “bores”) have been recorded. _ _ with thick ice available severe for traffic. The south part of the Gulf The range of the tides is about one foot at Copenhagen ; within of Bothnia is covered with every winter along the coasts, the Baltic proper ordinary tides are scarcely perceptible. There is, but rarely, if ever, in its centralicepart. is interrupted by however, a distinctly marked annual rise and fall due to meteoro- drifting ice from about the middle of Navigation to the beginning logical influences having a mean range of about 11-4 cm. (0'37 feet) of May, though the port of Hernbsand November has been known to remain at Travemiinde, and 13-9 cm. (0'46 feet) at Swinemiinde, the open during a whole winter. The northern is covered maximum occurring at the end of the summer rainy period m with traversable ice every third or fourth year. Quarken The northern part August. of Bothnia is frozen every winter. In the Guff ol The circulation of water in the Baltic proper must be con- of the Gulf the sea is closed to navigation by ice for about 150 days sidered apart from the circulation in the channels connecting it Finland the North Sea; and in this relation the ridge in the year; but navigation is now rendered possible throughout Circa la- with connecting the islands Falster and Moen with the the winter by the use of ice-breakers. tioa See references to different parts of the subject in the standard books coasts of Mecklenburg and Riigen must be taken as the dividing line. In the great basins and hollows from Rugen of Penck, de Lapparent, Suess, and others. Also Credner. to the Gulfs of Bothnia and Finland the upper layers of Die Entstehung der Ostsee. Leipzig, 1895.—De Geer. ton water, from 30 to 70 metres (16 to 38 fathoms) in thickness, Skandinaviens nivafbrdndringar under quartarperioden. Stock1888.—Sieger. Seenschwankungen und Strandverschieounhave ’almost the same salinity throughout. In these waters a holm vertical circulation is kept up by convection currents. Beneath qen in Skandinamen. Berlin, 1893.—Pettersson. “ Review of these layers are masses of salter water, through which a thermal Swedish Hydrographic Research,” Scottish Geographical Magazine, wave of small amplitude is slowly propagated to the bottom by 1894.—N. Ekholm. Om klimatets dndringar i geologisk och (h. N. D.) conduction. These strata are practically stagnant, deficient m historisk tid. Ymer. Stockholm, 1899. oxvo-en, and surcharged with carbonic acid. Their salter waters Baltic and Black Sea Canal. See must have been originally derived from outside, and must therefore have passed over the ridge between Falster and Mecklenburg, but Canals. their horizontal extension is checked by the ridges separating the Baltimore, in Maryland, one of the chief cities deep hollows in the Baltic from each other. The inflow to the
