518 
CUTTING- OF ISTHMUSES. 
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 have been actually made, but no 
work of this sort, possessing real geographical or even commer¬ 
cial importance, has yet 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 mainlands, 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 excava¬ 
tion below low-water mark—always a matter of great difficulty ; 
the dimensions of channels for sea-going ships must be much 
greater than those of canals of inland navigation; the height 
of the masts or smoke pipes of that class of vessels would 
often render 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 and the construction of ports at their termini 
would in general be difficult and expensive, and the harbors 
and the channel which connected them would be extremely 
liable to fill up by deposits washed in from sea and shore. 
Besides all this, there is, in many cases, an alarming uncer¬ 
tainty as to the effects of joining together waters which nature 
has put asunder. A new channel may deflect strong currents 
from safe courses, and thus occasion destructive erosion of shores 
otherwise secure, or promote the transportation of sand or slime 
to block up important harbors, or it may furnish a powerful 
enemy with dangerous facilities for hostile operations along the 
coast. 
