610 CUTTING OF MARINE ISTHMUSES. 
present and prospective voluntary controlling power over ter- 
restrial nature. 
Cutting of Marine Isthmuses. 
Besides the great enterprises of physical transformation of 
which I have already 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 cannot be said to 
be impracticable, though discouraged by the apprehension of 
disastrous consequences from the disturbance of existing natu- 
ral or artificial arrangements ; and there are still others, the 
accomplishment of which is ultimately certain, though for the 
present forbidden 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 gulf 
of Liimfjord in Jutland, referred to in the preceding chapter, 
nature has given a singular example of a canal which she alter- 
nately opens as a marine strait, and, by shutting again, converts 
into a fresh-water lagoon. The Liimfjord was doubtless origi- 
nally 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, 
