A WORKING EROSION AlOUHL FOR SCHOOLS 



709 



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A WORKING EROSION MODEL FOR SCHOOLS 



Uv Don Carlos Ellis 



WORKING model showing the 

 processes of erosion on defor- 

 ested slopes has been a feature 

 of exhibits made by the Forest Service 

 at recent expositions. It shows the 

 working out of the natural phenomena 

 so well, and is so simple and inexpen- 

 sive to construct, that a description is 

 here given of a similar model which 

 might be erected in schools for the use 

 of classes in nature study, elementary 

 agriculture, and physical geography. 



The model consists of two hills slop- 

 ing down into two valleys through 

 which two streams wind in and out 

 through farm land and lead into two 

 lakes at the front of the landscape. 

 (Fig. 1.) Ijoth hills are made of the 

 same kind of soil, that of the region in 

 which the model is erected, but one is 

 covered thickly with twigs, young trees, 

 or shrubs, to simulate a forest, under- 

 neath which is a heavy carpet of moss 

 representing the layer of leaves and 

 twigs which covers the ground in the 



real forest, while the other hill is bare 

 of all vegetation. 



By means of a suitable sprinkling de- 

 vice water in the form of rain is made 

 to fall with equal force upon the two 

 hills. On the forested slope its fall is 

 broken by the foliage and it drops 

 gently upon the moss-covered surface 

 of the ground. The moss and the soil 

 beneath, which is kept soft and porous 

 by the protective cover, quickly absorb 

 the rain and allow it to seep out as clear 

 water farther down the slope, thus 

 forming a mountain stream which ilows 

 through a green and fertile valley into a 

 clear lake at the lower end of the model. 



On the other slope the rain beating 

 down upon the unprotected and hard- 

 ened surface washes deep gullies in the 

 hillside, carries the soil into the turbid 

 stream which drains the valley below, 

 and thence into a muddy lake. The 

 erosion on the sloi)e loosens stones, 

 which are carried down upon the valley 

 farms; the silt deposited in the channel 



