AITTIQUITY OF IRRIGATION. 433 



terial and to objects of axtificial elaboration wbicb would other- 

 wise be worthless on account of the cost of conveyance ; they 

 supply from their surplus waters means of irrigation and ol 

 mechanical power; and, in many other ways, they contribute 

 much to advance the prosperity and civihzation 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 

 up, check and divert the course of natural currents, and dehvei 

 them at points opposite to, or distant from, their original outlets ; 

 they often require extensive reservoirs to feed them, thus retain- 

 ing through the year accumulations of water — which would 

 otherwise run off, or evaporate in the dry season — and thereby 

 enlarging the evaporable sm-face of the country ; and we have 

 already seen that they interchange the flora and the fauna ol 

 provinces widely separated by nature. All these modes of action 

 certainly influence climate and the character of terrestrial surface, 

 though our means of observation are not yet perfected enough 

 to enable us to appreciate and measure their effects. 



Antiquity of Irrigation. 



"We know little of the history of the extinct civilizations which 

 preceded the culture of the classic ages, and no nation has, in 



* Sismondi, speaking of the Tuscan canals, observes : " But inundations are 

 not the only damage caused by the waters to the plains of Tuscany. Eaised, 

 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, ster- 

 ilizes and turns to morasses fields which natui-e and the richness of the soil 

 seemed to have designed fur the most abundant harvests. 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 — which affects the taste of all its 

 products, even to the grasses, which the cattle refuse to touch — at last compel 

 the husbandman to abandon his fields and leave uncultivated a soil that no 

 longer repays his labor." — TaMeau de V Agriculture Toscane, pp. 11, 13. 

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