CUTTING OF MARINE ISTIMUSES. 611 
either permanently to maintain the barrier, or to remove it and 
keep a navigable channel constantly open. If the Liimfjord 
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 might produce very perceptible 
effects on the hydrography of the Cattegat. 
When we consider the number of narrow necks or isthmuses 
which separate gulfs and bays of the sea from each other, or 
from the main ocean, and take into account the time and cost, 
and risks of navigation which would be saved by executing 
channels to connect such waters, and thus avoiding the neces- 
sity of doubling long capes and promontories, or even conti- 
nents, it seems strange that more of the enterprise and money 
which have been so lavishly expended in forming artificial 
rivers for internal navigation should not have been bestowed 
upon the construction of maritime canals. Many such have 
been projected in early and in recent ages, and some trifling 
cuts between marine waters had been actually made; but before 
the construction of the Suez Canal, no work of this sort, pos- 
sessing real geographical or even commercial importance, had 
been effected. . 
These enterprises are attended with difficulties and open to 
objections which are not, at first sight, obvious. Nature guards 
well the chains by which she connects promontories with main- 
lands, and binds continents together. Isthmuses are usually 
composed of adamantine rock or of shifting sands—the latter 
being much the more refractory material to deal with. In all 
such works there is a necessity for deep excavation below low- 
water mark—always a matter of great difficulty; the dimen- 
sions of channels for sea-going ships must be much greater 
than those of canals of inland navigation; the height of the 
masts or smokepipes of that class of vessels would often ren- 
der bridging impossible, and thus a ship-canal might obstruct a 
communication more important than that which it was intended 
to promote; the securing of the entrances of marine canals 
