GEOGRAPHICAL EFFECTS OF CANALS. 359 
ried upon a high level across low ground, often injures the 
adjacent soil, and is prejudicial to the health of the neighbor¬ 
ing population ; and it has been observed in Switzerland, that 
fevers have been produced by the stagnation of the water in 
excavations from which earth had been taken to form embank¬ 
ments for railways. 
If we consider only the influence of physical improvements 
on civilized life, we shall perhaps ascribe to navigable canals a 
higher importance, or at least a more diversified influence, 
than to any other works of man designed to contrdl the waters 
of the earth, and to affect their distribution. They bind dis¬ 
tant regions together by social ties, through the agency of the 
commerce they promote ; they facilitate the transportation of 
military stores and engines, and of other heavy material con¬ 
nected with the discharge of the functions of government; they 
encourage industry by giving marketable value to raw ma¬ 
terial and to objects of artificial elaboration which would other¬ 
wise be worthless on account of the cost of conveyance ; they 
supply from their surplus waters means of irrigation and of 
mechanical power ; and, in many other ways, they contribute 
much to advance the prosperity and civilization of nations. Nor 
are they wholly without geographical importance. They some¬ 
times drain lands by conveying off water which would other¬ 
wise stagnate on the surface, and, on the other hand, like aque¬ 
ducts, they render the neighboring soil cold and moist by the 
percolation of water through their embankments ; * they dam 
* Simonde, speaking of the Tuscan canals, observes: “ But inundations 
are not the only damage caused by the waters to the plains of Tuscany. 
Raised, as the canals are, above the soil, the water percolates through 
their banks, penetrates every obstruction, and, in spite of all the efforts 
of industry, sterilizes and turns to morasses fields which nature and the 
richness of the soil seemed to have designed for the most abundant har¬ 
vests. In ground thus pervaded with moisture, or rendered cold, as the 
Tuscans express it, by the filtration of the canal water, the vines and the 
mulberries, after having for a few years yielded fruit of a saltish taste, rot 
and perish. The wheat decays in the ground, or dies as soon as it sprouts. 
Winter crops are given up, and summer cultivation tried for a time ; but 
the increasing humidity, and the saline matter communicated to the earth 
