SOME SETTLED PRINCIPLES. 129 



thin sheet over a grassy sod has a different effect from that 

 of water passing over uncultivated soil. It does not wash 

 the soil nor carry off soluble matter from it, but it is it- 

 self filtered of whatever matter it contains that can be 

 appropriated by the roots of the grass. 



The width of the levels that may be irrigated is very 

 irregular, and depending greatly upon the character of the 

 surface. The larger the breadth the cheaper the process 

 of preparing the surface, because the expense of forming 

 the embankments, canals, sluices, and drains, is divided 

 over a larger number of acres, and the cost per acre is 

 diminished. It is cheaper to enclose a large area 100 

 acres for instance although the works maybe heavier and 

 more costly, than a smaller one of 10 acres with much 

 lighter works. In laying out water meadows, this con- 

 sideration should not be neglected, and the largest area 

 possible should be enclosed. Some of the dikes enclosing 

 the English and Italian water meadows are not less than 

 20 feet in hight, but hundreds of acres are brought under 

 irrigation by them. In such cases the works are massive, 

 costly, and built to last for ages. Smaller meadows may 

 not require embankments of more than one to three feet 

 in hight, and the earth for these may be procured from 

 the drains which carry off the surplus water, and which 

 are necessarily of ample size. In making the banks it 

 will be found the cheapest plan to dig the drains large 

 enough to supply all the earth needed for the banks ; the 

 extra ground used will be of very little importance com- 

 pared with the expense of bringing earth from a distance 

 for the construction of the banks. 



A water meadow, or at least each section of a meadow 

 in one enclosure, must necessarily be carefully leveled. 

 The most perfect meadow is one that has a perfectly level 

 surface between the banks, so that it can be covered even- 

 ly with six inches of water. The water may be flowed 

 'over the surface of a meadow of this character, and kept 



