150 ACTION OF THE SOIL ON PLANTS. 



form marshes : districts of this description abound on the 

 coast of the Adriatic. Sometimes they deposit their solid 

 contents in one large bank, when their current is first re- 

 pulsed by the waves of the sea, and form at the mouth of 

 the river a plain or Delta : such is the Delta at the mouth 

 of the Nile. 



Caroline. And if we may be allowed to compare small 

 things to great ones, such I suppose is the origin of the 

 Delta or low land at the mouth of the Rhone, on enter- 

 ing the lake of Geneva from the Valais. And the Isle of 

 Camarque, formed by the deposition of the waters of the 

 Rhone at its entrance into the sea, offers a still more 

 striking example. 



Mrs. B. Sometimes, the rivers have sufficient power 

 to struggle against the resistance of the waves, and do 

 not deposit their mud and sand, till they have advanced 

 to some little distance in the sea ; when their waters, 

 broken and divided by the waves, precipitate their cargo 

 in separate spots, forming a number of small islands ; 

 hence the origin of those on which Venice is built. 



We have prolonged our conversation rather beyond 

 bounds to-day ; I have but one more remark to make to 

 conclude this subject. 



When it is required to resist the force of an irregular 

 mountain-torrent, a number of small embankments is 

 preferable to one large dyke, however strong ; for during 

 violent rains there is some danger of the dyke being car- 

 ried away, while several small embankments successively 

 break the force of the waters. 



CONVERSATION XII. 



ON THE ACTION OF THE SOIL ON PLANTS. 



Mrs. B. Our last conversation was upon water : to- 

 day we shall change the subject to dry land. It has been 

 asserted, that earth was not absolutely essential to vege- 

 tation, because there are some plants which do not re- 



830. -What instances of illustration are named 1 ? 831. What ones 

 in Europe does Caroline mention'? 832. How were the islands on 

 which Venice is built formed 1 ? 833. What is said of the earth as be- 

 ing essential to vegetation 1 ? 



