CUTTING OF MARINE ISTHMUSES. 585 



CuUmg of Marine IstJmmses. 



Besides the great enterprises of physical transformation of 

 which I have abeady spoken, other works of internal improve- 

 ment or change have been projected in ancient and modern 

 times, the execution of which would produce considerable, and, 

 in some cases, extremely important, revolutions in the face of 

 the earth. Some of the schemes to which I refer are evidently 

 chimerical ; others are difficult indeed, but can not be said to 

 be impracticable, though discouraged by the apprehension of dis- 

 astrous consequences from the disturbance of existing natural or 

 artificial arrangements ; and there are still others, the accomphsh- 

 ment of which is ultimately certain, though for the present for- 

 bidden by economical considerations. 



Nature sometimes mocks the cunning and the power of man 

 by spontaneously performing, for his benefit, works which he 

 shrinks from undertaking, and the execution of which by him 

 she would resist with unconquerable obstinacy. A dangerous 

 sand-bank, that all the enginery of the world could not dredge 

 out in a generation, may be carried off in a night by a strong 

 river-flood, or by a current impelled by a violent wind from an 

 unusual quarter, and a passage scarcely navigable by fishing-boats 

 may be thus converted into a commodious channel for the largest 

 ship that floats upon the ocean. In the remarkable guK of Liim- 

 f jord in Jutland, referred to in the preceding chapter, nature has 

 given a singular example of a canal which she alternately opens 

 as a marine strait, and, by shutting again, converts into a fresh- 

 water lagoon. The Liimf jord was doubtless originally an open 

 channel from the Atlantic to the Baltic between two islands, but 

 the sand washed up by the sea blocked up the western entrance, 

 and built a wall of dunes to close it more firmly. This natural 

 dike, as we have seen, has been more than once broken through, 

 and it is perhaps in the power of man, either permanently to 

 maintain the barrier, or to remove it and keep a navigable chan- 

 nel constantly open. If the Liimf jord becomes an open strait, 

 the washing of sea-sand through it would perhaps block some of 

 the belts and small channels now important for the navigation 

 of the Baltic, and the direct introduction of a tidal current 

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