1884.] THE ARIDITY OF SPAIN. 123 



Here I am acting the part of the narrator only ; hut I do this with 

 approval of what has been done. 



The loss of the rainfall by evaporation has proved to be very great; 

 and it can only be partially arrested by sylviculture, and the 

 conservation of existing forests. Much more manifest is the 

 great loss of rainfall in the waters carried off by rivers to the sea. 

 It is a prevalent idea that a land is watered by its rivers. The 

 function of rivers is to drain the land. It is not stagnant water 

 which promotes vegetation, but water absorbed liy the soil ; and the 

 natural drainage of land is the carrying off to these aqueducts all 

 moisture in the soil in excess of what is thus absorbed. True, the 

 rivers often carry the surplus rainfall of a higher-lying land through 

 a region which suffers from lack of rain or dew ; and this land may 

 be made to benefit by it, if it be led off to water its surface. 



This is being done here lay works of irrigation, under the direction 

 of the Forest Engineers. The work was begun in the days of Iloman 

 domination, if not before. It was carried out extensively under the 

 Moors, whose regulations in regard to the water-supply are in some 

 places still in force. The Forest Engineers no more claim originality 

 for irrigation in Spain than they do for sylviculture there. But it 

 is the Forest Engineers who have perfected the existing works. 



In these, water is led off by canals from the rivers at suitable 

 points. Where necessary, and suitable facilities exist, this is stored in 

 large reservoirs, and it is led off in appropriately-constructed water- 

 leadings to the lands to be irrigated. The surplus is collected and 

 led farther, being in every case supplied under efficient regulations, 

 while in some cases, either before or after being so employed, 

 it is utilized in its descent to a lower level in giving motion to mills. 



To a limited extent, where two rivers feed a reservoir, an arrange- 

 ment similar to what was introduced into China more than four 

 thousand years ago, shortly after the flood, is made use of, whereby 

 one river in flood may send its surplus water down the bed of a 

 river in which the supply is deficient. 



Such hydraulic engineering may be somewhat incongruous with 

 our ideas of the work of a forester ; but many such matters are 

 embraced by the comprehensive department of forest science, as that 

 science is taught in some of the Schools of Forestry on the Continent. 

 But the mention made of rivers in flood brings us back to what more 

 strictly pertains to forestry as that term is conventionally made use 

 of by us. 



Spain is occasionally subjected to the destructive effects of 

 inundations ; such inundations as Sir Thomas Dick Lauder has 

 described in his Account of the Great Floods of August 1829, in the 

 Province of Moray and Adjoining Districts. 



