GORDON] A FIELD TRIP TO THORNTON 83 



In the valley bottom the student finds fine sediment on the 

 Hood-plain and terraces and learns that those features may be the 

 work of both erosion and deposition. He needs little assistance 

 now to explain this situation or the presence of sand bars in the 

 channel. But when he approaches the stream and finds that 

 the flood-plain is higher immediately along the bank than back 

 from the river he discovers a new and often a perplexing prob- 

 lem. This feature is a natural levee (Fig. 2). Why in flood 

 times, did the stream deposit more along its banks than farther 

 back? The fact that the overflowing current is checked there 

 first, by coming in contact with vegetation and the quiet flood 

 waters is easily within his reasoning ability. 



Life Relations. 



During all field work the relationship of the work of running 

 water to plant and animal life, especially human life, should be 

 kept constantly before the student. It is desirable in the study 

 of each feature to raise the question of its importance, both posi- 

 tive and negative. The agricultural value of flood-plains, deltas, 

 and alluvial fans ; the use of streams for power, commerce, boun- 

 dary lines, irrigation, pleasure, sewage disposal, and for drinking 

 water, is known to most boys and girls, yet it is doubtful if they 

 have ever really correlated them in the field. 



A Field Trip to Thornton, Illinois 



Phyllis Gordon. 



On our way to Thornton we saw the old lake Michigan 

 outlet, and shore line. The outlet is a long, wide flat, bounded 

 on either side by low hills which mark the old shore line. 



The topography of the Thornton region is slightly rolling, 

 and is called a ground moraine. The debris which the glacier 

 deposited when it melted back is the origin of the hills. The 

 soil is made of sand, clay, and loose rocks of every kind and 

 size. The region is in youth, while the river is in a slightly later 

 period of development. Running water in this case has not cut 

 out the hills, the glacier deposited its load in hill form. 



Erosion by running water is well shown in this region. The 

 strongest current is on the outside of a bend and therefore, 

 there is where the most erosion will occur. At one place the river 

 meandered over a good sized flood plain. On one side the bank 

 rose almost perpendicularly, but on the other there was a small 



