AND PROTECTION OF AGRICULTURAL LAND 29 



and rushes will prevail. The surfaces of these naturally formed 



racts of ground are, as may be gathered from what has been said, 



n a pretty high level. I found the marshes of Salt-area, 



Coleway, Ovangle, and Overtoil on the Lune, and of Clifton, 



Howie, and Hesketh on the Eibble, to average about a foot below 



high water of ordinary spring tides. 



In connection with this gradual accretion and formation of 

 land, and the sudden changes which, if unprotected, it some- 

 times is destined to undergo, it may be interesting to the geo- 

 logist to state as having come under my own observation, that a 

 sandbank covered by every tide may, by a happy diversion of 

 the river, become in a few years useful pasture land ; while, on 

 the other hand, by another capricious change of the river's 

 course, the apparently permanent pasture meadow, the growth 

 of years, may suddenly disappear in a few tides, and the spot 

 where cattle have been grazing to-day may to-morrow once more 

 be the main channel of the river. Instances of such sudden 

 changes I have witnessed both on the Eibble and the Lune 

 before the courses of these rivers were controlled and directed by 

 proper works. 



In my treatise on "Kiver Engineering" I have shown that 

 many cases the interests of navigation and agriculture are 

 dentical, and that the erection of training walls, such as shown 

 in fig. 7, by guiding the river, and thus improving the naviga- 

 ion, may, at the same time, greatly promote the interests of 

 iculture, by rendering such wholesale destruction as that to 

 which I have alluded impossible, and by converting reclaimed 

 marsh land into permanent property. 



On the Tay and at other places the process of warping is 



