FILLING UP OF LAKES. 287 



will be filled up and formed into a region of level green 

 fields." 



John was much surprised at this statement, and asked 

 how it would be done. Lawrence explained to him that 

 the lake was a vast hollow in the land filled with water, 

 and that the river was all the time bringing down sand, 

 and pebbles, and sediments of various kinds from the coun- 

 try above ; and that, though some of these materials were 

 carried through and borne out through the lower end of 

 the lake, and so onward into the sea, some portion must 

 necessarily be left behind, and in process of time the whole 

 lake must be filled. 



"Nonsense!" said John; "such a great lake as this 

 could never be filled in this way. There would not be 

 sediment enough brought down to fill it not in a thou- 

 sand years !" 



" Perhaps not," said Lawrence ; " but if the river could 

 not fill it in a thousand years, it might in ten thousand." 



" No," rejoined John, " I don't believe it would fill it 

 even in ten thousand." 



" Then ten million," replied Lawrence. " You can have 

 as many years as you want. There are plenty of them 

 coming. If there is any deposit at all left in the lake, and 

 nothing to take it away, the lake must some time or other 

 become filled up." 



The conversation on this subject was continued between 

 Lawrence and John for some time, and in the course of it 

 Lawrence explained somewhat at length the manner in 

 which natural depressions in the surface of the land which 

 occur in the course of the current of a river, or w r idenings 

 of the valley through which it flows, and which at first be- 

 come, of course, so many reservoirs of water supplied by 

 the river, thus forming lakes, are gradually filled up by de- 

 posits of sand and soil, so as to form in the end broad plains 



