Soil-Bi)idcrs 53 



useful service in the Bermudas by stoppinp^ the fine 

 white coral-sand of the coast from invading and bury- 

 ing the neighbouring gardens. 



Plants of the convolvulus family are equally useful 

 on the coast of Ceylon, where the rivers, flowing 

 rapidly down from lofty hills, brin.i; with them heavy 

 loads of sand and mud. Under ordinary circumstances, 

 since the Bay of Bengal is not, like the Mediterranean, 

 a tideless sea, these would be carried away and de- 

 posited some miles from the coast. But this is pre- 

 vented by the ocean-currents, which set towards the 

 island, and not only drive back what the rivers bring 

 down, but add to them similar loads of their own. 

 Accordingly, the sand and mud of the rivers, unable to 

 escape further, are piled up in bars along the shore, 

 and these, when once begun, rapidly increase in size 

 until they rise above the water, and form long em- 

 bankments reaching for many miles, with the river 

 flowing behind, and occasionally bursting through 

 them. 



These bars, though a mile or two and even more in 

 width, are not very solid at first, but they are presently 

 sown with such plants as do not mind salt water, and 

 the roots soon penetrate and mat together in such a 

 way as to prevent the soil being washed away. The 

 drier sand on the top of the bank is protected from 

 wind and rain by creeping plants, among which is one 

 of the great bindweeds already mentioned, which covers 

 the surface down to the water's edge, with its long, 

 trailing branches pegged down at each joint, as already 

 described. 



When the sand has been consolidated and improved 

 by the growth and decay of these and such-Hke plants, 



