Instead of cutting a canal from the head of the delta of the San
Juan to the sea, as has been proposed, the Colorado branch might be
straightened, and dredged to the required depth. Higher up, the
Torre, Castillo, and Machuca Rapids form natural dams across the
river. These might be raised, locks formed round them, and the
water deepened by dredging between them. In this way the great
expense of cutting a canal, and the fearful mortality that always
arises amongst the labourers when excavations are made in the
virgin soil of the tropics, especially in marshy lands, would be
greatly lessened between the lake and the Atlantic. Another great
advantage would be that the deepening of the river could be
effected by steam power, so that it would not be necessary to bring
such a multitude of labourers to the isthmus as would be required
if a canal were cut from the river; the whole track, moreover,
passes through virgin forests rich in inexhaustible supplies of
fuel.* (* The commission appointed by the United States Government
to examine into the practicability of making a canal across the
isthmus reported in favour of the Nicaraguan route, and the work
was begun at Greytown in 1889. But after an expenditure of 4,500,
000 dollars, the scheme was abandoned, for political reasons, in
favour of the Panama route.)

San Carlos is a small town at the foot of the great lake, where it
empties its waters into the San Juan river, its only outlet to the
ocean. On a hill behind the town, and commanding the entrance to
the river, are the ruins of a once strong fort built by the
Spaniards, the crumbling walls now green with the delicate fronds
of a maiden hair fern (Adiantum). The little town consists of a
single rugged street leading up from the lake. The houses are