276 On Irrigation. 



towns and villages through which it passes ; and is thus pro- 

 ductive, not only of temporary, but of permanent improve- 

 ment. 



Sea-water also, where it can be employed for that purpose 

 in moderate quantities, or made use of within embanked 

 marshes, is applicable to the purposes of irrigation. It con- 

 tains, more especially near the land, not only animal and 

 vegetable substances, but also saline mixtures in solution. 

 The utility of salt marshes to diseased horses, and their 

 acting as a restorative to sheep in danger of, or infected by, 

 that fatal malady the rot, is well known. These ideas are 

 corroborated by an observation, that the meadows near the 

 mouth of the Severn, where salt water is spread over the lands 

 by the tide, are grazed, instead of being mown, and are ac- 

 counted the best possible pasture for horses and cattle that 

 require rest and spring physic ( 4I<5 ). 



In regard to waters much impregnated with iron, they 

 were formerly supposed totally unfit for the purposes of irri- 

 gation ; but it is now fully proved, by the accurate experi- 

 ments of an able chemist, and by the extraordinary growth 

 of grasses in Prisley meadow, in Bedfordshire, that ferrugi- 

 nous waters are friendly to vegetation, when properly ap- 

 plied ( 4I? ). Springs, however, or water impregnated with 

 other mineral substances, as lead or copper, never do good ; 

 and it is well known, that waters of that description, after 

 they have been brought into fields, by levels cut at a consi- 

 derable expense, have again been diverted, and suffered to 

 flow in their original channels ( 4l8 ). 



Waters that are impregnated with the juices that flow 

 from peat-mosses, are considered by many, not worth ap^ 

 plying to the soil ( 4I9 ). It is objected to them, that they are 

 soon frozen; that they convey no material nutriment; 

 and that they are commonly loaded with such antiseptic sub- 

 stances as will retard, instead of promoting vegetation ( 42 ). 

 It is urged, on the other hand, that a want of sufficient slope 

 in the meadow, or of proper management in regard to the 

 water, may have occasioned the disappointments experienced 

 in some cases, when bog-waters have been applied ( 431 ). 



5. Of the Soil and Subsoil. 



Irrigation is not restricted to any particular description of 

 soil. Land naturally wet, may be greatly improved by it, 

 when accompanied by drainage ; and it is equally beneficial 

 to that which is dry ( 4 * 2 ). 



