750 Home Nature-Study Course. 



(9). If you can see the place where the brook empties into a pond 

 or lake, how does it make the waters of the latter look after a storm? 



(10). What is the water of the brook doing to give this appearance, 

 and why? 



(11). What becomes of the soil dropped by the brook as it enters a 

 pond or lake? 



(12). Do you know of any points of land extending out into a lake 

 or pond where the stream enters it? 



(13). What is a stream delta? 



Facts for the Teacher. — The little experiment suggested to begin this lesson 

 should show the pupils clearly the following points : That it is through motion that 

 water takes up soil and holds it in suspension. The tendency of still water is to 

 drop all the load which it is carrying and it drops the heaviest part first. You 

 will find the pebbles at the bottom, the sand and gravel next and the fine mud on 

 top. The water may become perfectly clear in the jar and yet when stirred a little 

 will become roily again because of the movement. Every child who wades in the 

 brook knows that the sides and the still pools are more comfortable for the feet 

 than is the center of the stream under the swiftest current. This is because where 

 the water' is less swift at the sides it deposits its mud and makes a soft bottom 

 while under the swifter part of the current mud is washed away leaving the larger 

 stones bare. For the same reason the bottom of a stream crossing a level field 

 is soft because the silt washed down from the hills by the swift current is dropped 

 when the waters come to a more quiet place. If the pupils can build a dam that 

 will hold across a stony brook bottom for two or three months in the fall or spring 

 when the brook is flooded they will be able to note that the stones will be more 

 or less covered with soft mud because the dam stopping the current causes the 

 water to drop its load of silt. It would have to be a very recently made still pool 

 in any stream which would not have a soft mud bottom. The water at times of 

 flood is forced to the side of the streams in eddies and its current is thus checked 

 and its load of mud dropped. It should be noted that at points where the brook 

 is narrowest the current is swiftest, and where the current is swiftest the bottom 

 is more stony. Another thing you might point out; where there is a bend in the 

 stream the brook digs deeper into the bank where it strikes the curve, and much 

 of the soil thus washed out is removed to the other side of the stream where the 

 current is very slow and there drops it. (See "Introduction to Physical 

 Geography," Gilbert and Brigham, pp. 51 and 52.) If it is possible note where the 

 muddy stream empties into a pond or lake the waters of the latter will be made 

 roily for some distance out, but beyond this the water will remain clear. The 

 pupils should be made to see that the swift current of the brook flowing into 

 a still pond is checked and thus drops its load. It does this year after year and 

 thus builds up a point extending out into the lake or pond. It is thus that the 

 great river deltas are built up. 



References. — " The Brook Book," :Mary Rogers Miller ; " Brooks and 

 Brook Basins," Frye ; " Up and Down the Brooks," Bamford ; " Physical 

 Geography," Tarr ; " Introduction to Physical Geography," Gilbert & 

 Brigham. 



