400 
BASINS IN PERU AND SPAIN. 
yards, or less than one ninth part of what I suppose to be 
required. The case of the Ardeche is no doubt an extreme 
one, both in the topographical character of its basin and in its 
exposure to excessive rains; but all destructive inundations 
are, in a certain sense, extreme cases also, and this of the 
Ardeche serves to show that the construction of reservoirs is 
not by any means to be regarded as a universal panacea 
against floods. 
Nor, on the other hand, is this measure to be summarily 
rejected. Nature has adopted it on a great scale, on both 
flanks of the Alps, and on a smaller, on those of the Adiron- 
dacks and lower chains, and in this as in many other instances, 
her processes may often be imitated with advantage. The 
validity of the remaining objections to the system under dis¬ 
cussion depends on the topography, geology, and special cli¬ 
mate of the regions where it is proposed to establish such 
reservoirs. Many upland streams present numerous points 
where none of these objections, except those of expense and of 
danger from the breaking of dams, could have any application. 
Reservoirs may be so constructed as to retain the entire pre¬ 
cipitation of the heaviest thaws and rains, leaving only the 
ordinary quantity to flow along the channel; they may be 
raised to such a height as only partially to obstruct the surface 
drainage; or they may be provided with sluices by means of 
which their whole contents can be discharged in the dry sea¬ 
son and a summer crop be grown upon the ground they cover 
at high water. The expediency of employing them and the 
mode of construction depend on local conditions, and no rules 
of universal applicability can be laid down on the subject. 
It is remarkable that nations which we, in the false pride 
of our modern civilization, so generally regard as little less 
than barbarian, should have long preceded Christian Europe in 
the systematic employment of great artificial basins for the 
various purposes they are calculated to subserve. The ancient 
Peruvians built strong walls, of excellent workmanship, across 
the channels of the mountain sources of important streams, 
and the Arabs executed immense works of similar description, 
