BALTIC SEA 97 hollows or troughs. The first, or Bornholm deep, lies east the island of Gland; this is entirely cut off to the south of the island of Bornholm, and is separated from the next, and east by a bank which sweeps eastward and northward or “ Gothland ” deep, by the “ Middelbank.” Beyond from near Karlskrona, and on which the island of Gothland stands, but it communicates at its northern end with the Gothland deep, and near the junction THE BALTIC opposite Landsort is the deepest Scale of Engl Miles hole in the Baltic (420 metres = 230 fathoms). Depths in feet An unbroken ridge, extending from Stockholm to Hango in Finland, separates the Baltic basin proper from the depression between Sweden and the Aland Isles, to which the name Aland Sea has been given. North of the Aland Sea a ridge defines the southern edge of another depression, the Bothnian Sea, which in turn is separated from the most northerly division, the Gulf of Bothnia, by a ridge across the narrow Quarken Strait. The Gothland deep may be said to extend directly into the Gulf of Finland, an arm of the Baltic, running eastwards for about 250 miles, and separating Finland from Esthonia. Between Esthonia and Courland is the Gulf of Riga, a shallow inlet of roughly circular form, about 100 miles in diameter, and nowhere more than 27 fathoms deep. According to recent computations the total area of the Baltic, including the Skagerrak and Kattegat, is 430,970 sq.km. (= 166,397 sq. in.), and its volume 28,732 cub. km. ( = 6907 cub. in.), giving a mean depth of 36 fathoms, which is markedly less than that of any other arm of the sea of similar area. In the deeper hollows in the south part of the Baltic the bottom consists almost invariably of either soft brown or gray mud or hard clay, while on the shallow banks and near the low coasts fine sand —of white, yellow, or brown colour —with small pebbles, is usually found. Map of the Baltic Sea At the time of the last great subsidence, in glacial times, an arm of _ the sea extended phoI eomoracross Sweden, °8ysubmerging a great part of the littoral up to the Gulf of Bothnia, and including the present lakes Wener, Hjelmar, and Malar. During this period the waters of the northern Baltic were sufficiently salt for oysters to flourish. The subsequent Section of Baltic on Line A to T showing Salinity. upheaval restricted direct with the open the “Middelbank” the “ Danziger Tiefe,” an isolated sea to the Danish channels, and communication the Baltic waters became epression, lies to the south-east, while to the north-east the fresher: the oyster disappeared, but a number of cold saltGothland basin, the largest and deepest of all, extends water fishes and crustaceans, and even seals, became acclimatized. It has been suggested that the presence of the remains north-eastwards to the Gulf of Finland. Along the of animals indicates a communication to the north with > Medish coast a deep channel runs northward from outside thethese Arctic Ocean ; but in view of the severe climatic conditions S. II. — I T
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