228 IRRIGATION. 



would serve to encircle the whole earth with a belt 6 feet 

 in hight and thickness. One embankment of solid 

 masonry, strongly cemented together and covered with 

 earth, exists in Ceylon, which is 15 miles long, 100 feet 

 wide at the base, slopes to a top width of 40 feet, and 

 extends across the foot of a spacious valley. In Europe 

 there are many reservoirs for irrigation. In Spain there 

 are a large number ; Italy has most of any European 

 country ; in France there are many of considerable extent, 

 one contains 500,000 cubic yards, another 4,000,000 yards, 

 and hundreds contain from 20 up to 50,000 cubic yards. 

 In our own country, where we have seen a railroad system 

 so vastly and successfully extended, it cannot be doubted, 

 that at some time not far in the future, equally costly 

 and valuable works may be constructed, having for their 

 object the reclamation of fertile soils from aridity by 

 bringing to them a supply of water which now flows 

 away uselessly. By impounding the winter rainfall of 

 thousands of valleys, or the melting snow from thousands 

 of hills, floods may be prevented and a store of water be 

 accumulated for use in the rainless season, which may 

 bring into productiveness millions of acres of now waste 

 lands. The manner of making these storage reservoirs 

 is to throw across the outlet of a valley or of a series of 

 valleys connected together, a dam of sufficient hight and 

 strength, furnished with outlet pipes, which discharge, 

 either constantly or intermittently, into a canal. The 

 proper construction of the dam has been already treated 

 of ; it will now only be necessary to consider some im- 

 portant and pertinent characteristics of the valleys them- 

 selves. 



At fig. 110 is shown a system of valleys, which have 

 but one outlet at the narrow neck where the dam is 

 thrown across. This is a typical example of a most 

 favorable opportunity for constructing an irrigation reser- 

 voir. In some cases it may be necessary to make more 



