114 AGRICULTUHE. 



subsided into quiet oblivion. The practice so derided and 

 maligned has advanced with wonderful strides. We 

 remember the days of 1 5 inches ; then a step to 20 ; a 

 stride to 30; and the last (and probably final) jump to 50, 

 a few inches under or over. We have dabbled in them 

 all, generally belonging to the deep section of the day. 

 We have used the words *' probably final " because the 

 first advances were experimental, and, though they were 

 justified by the results obtained, no one attempted to 

 explain the principle on which benefit was derived from 

 them. The principles on which the now prevailing depth 

 is founded, and which we believe to be true, go far to show 

 that we have attained all the advantages which can be 

 derived from the removal of water in ordinary agriculture. 

 We do not mean that, even in the most retentive soil, 

 water would not get into drains which were laid somewhat 

 deeper ; but to this there must be a not very distant limit, 

 because pure clay, lying below the depth at which wet and 

 drought applied at the surface would expand and contract 

 it, would certainly part with its water very slowly. We 

 find that, in coal mines and in deep quarries, a stratum of 

 clay of only a few inches thick interposed between two 

 strata of pervious stone will form an effectual bar to the 

 passage of water ; whereas, if it lay within a few feet of 

 the surface, it would in a season of heat and drought 

 become as pervious as a cullender. But when we have 

 got rid of the cold arising from the evaporation of free 

 water, have given a range of several feet to the roots of 

 grass and cereals, and have enabled retentive land to filter 

 through itself all the rain which falls upon its surface, we 

 are not, in our present state of knowledge, aware of any 

 advantage which would arise from further lowering the 

 surface of water in agricultural land. Smith, of Deanston, 

 first called prominent attention to the fertilizing effects of 

 rain filtered through land, and to evils produced by allow- 

 ing it to flow off the surface. Any one will see how much 

 more effectually this benefit will be attained, and this evil 



