40 HANDBOOK OF NATURE STUDY 



ing; that of the Mississippi advances a mile in sixteen 

 years. 



23. The Sand Bank. 



Visit a sand bank formed by a river or creek. If that is not acces- 

 sible, the sand spread out below a washout will illustrate the lesson. 

 Have a gardener's trowel or spade to dig into the sand. 



Field lesson. From observations which we made some 

 time ago, you can tell me how this sand bank was formed. 

 Of course, the river brought the material from farther up 

 the stream and deposited it here. If I dig a small hole 

 into the sand, you will see that it is arranged in definite 

 layers or strata. As water spreads the fine sand or mud 

 quite uniformly, it could hardly be otherwise. Now we 

 will go back and dig a hole on the high bank, where the 

 water reaches only at the time of high freshets. Here, 

 also, we find the soil quite distinctly stratified. After high 

 water I have seen this bank covered with a layer of mud. 

 As the river has been here thousands of years, this must 

 have occurred many times, and in that way this bottom 

 land has been formed. Rivers and creeks, however, are not 

 only depositing sediment ; they are also cutting away their 

 banks all the time. Often they deposit on the left side 

 when they cut on the right, and vice versa. By and by 

 some of the soil is washed into the ocean, as we have 

 learned. Most of that soil has been taken up and deposited 

 again and again before it reaches the river's mouth. 



Now look at the rock which you see exposed on the bank 

 there. It is arranged in layers, which we can easily trace. 

 In the stone quarries which we visited we found the rock 

 arranged in layers. Wherever water runs over these rocks, 

 it cuts some of it away, turns it over and over, and grinds 

 it up into soil. 



Observations. Try to find the flowers of grain and of grasses. 



