Page:Encyclopædia Britannica, Ninth Edition, v. 3.djvu/312

296 now been stated, that the increase of height and dimensions which has been observed in the reefs and inlets of the Bkar 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 débris. 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 con troverted by other authorities, was embraced by Linnaeus. It is now clear that many of the facts by which it was sup ported 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 GOO 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. Hence 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 must 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 183G. 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 GO 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 Rack, 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 discharge themselves into it is greatly reduced by the freezing of their sources ; and this is, of course, especially the caso 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, is 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 happens during the spring and summer months, although the excess 