THE SCIENCE OF OBSERVATION. 



465 



the lake the outflowing water appears clear as crystal; the sediment 

 brought in by the river has manifestly been deposited in the lake, 

 as was the case in our little pool. The marsh at the upper end, of 

 course, is merely another delta, slow growing in this instance, grass- 

 covered, but as surely encroaching on the water area as in the earlier 

 examples. When an entering stream is normally of great transport- 

 ing power, owing to steep slopes down which it rushes, the form of 

 its delta is not unlike the one first described. 



With the data already gathered, we can not escape from the con- 

 clusion that the growth going on at the head of the lake will in time, 



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Fig. 4. — A Common Form of Large Delta. 



if present conditions continue to exist, push its way forward until it 

 has occupied the whole water area. The sediment which is now de- 

 posited therein will then be transported across the plain, and will 

 be carried along until another-. body of water is reached. Further 

 search will bring to light the fact that there are plenty of examples 

 showing all stages between the simple delta and the completely filled 

 lake. The innumerable marshes and meadows which characterize 

 the northern part of the United States are fine examples of lakes 

 which have perished in this manner. 



Our next excursion will be made to the locality shown in Fig. 4, 

 which is a sketch of a large delta occurring at a considerable 

 height above the general level of the country, although at the present 



