CIRCUMSTANCES MODIFY ITS ACTION. 145 



able. It has been ascertained that in this country, on an 

 average, each person consumes about 14 Ib. of salt every year. 

 A large portion of this must find its way into the refuse of towns ; 

 and though much of it is emptied into the common sewers, 

 and thence into the rivers, and so is sent back to the sea, yet a 

 considerable proportion of it must be conveyed with the solid 

 manure to the adjoining land. This may be enough to explain 

 why the farmer of such land should, upon trial, derive no money 

 benefit from the direct application of salt. 



3. The geological structure of the country. The presence of 

 marine formations, or of deposits of salt, or the occurrence 

 of salt springs, may also render the addition of salt unpro- 

 fitable. 



4. The previous use of salt upon the same land may render 

 it unnecessary in after years. It has indeed, in some cases, 

 been observed that the same land which gave a large profit 

 upon its application one year, showed no improvement from its 

 use in the next succeeding year. 



5. The use of salt in feeding may also render it unnecessary. 

 Where the practice exists of salting hay, of giving salt to the 

 stock, of leaving a piece of rock-salt in the feeding trough for 

 the cattle or sheep to lick, the manure which is made must 

 contain much salt. This will be in great part carried to the 

 land, and will thus supply more or less completely any natural 

 deficiency of this substance which the soil may exhibit. 



6. The climate and season will materially interfere with its 

 action. In dry climates, where seasonable rains seldom fall, 

 salt will rarely do anything but injury. In such climates the 

 saline matter, natural to the soil, is brought to the surface by 

 the waters which rise from beneath, and accumulates there so as 

 often to be a chief cause of the destruction of the crops or 

 natural herbage. An unusually dry season in our own climate 

 has a similar effect. Thus in 1844, which was an unusually 

 warm and dry summer, Mr John Wilson of Penicuick, in Mid- 

 Lothian, applied salt to the grass he cut for hay in two fields, 

 with the following results compared with nitrate of soda and 

 saltpetre : 



