406 REPORT OF THE COMMISSIONERS OF 



3 oil-Fixation. 



When unrestrained by a forest cover, both wind and water play havoc with soil. 

 Gales of wind and downpours of rain are not required to produce this damage. It 

 occurs with almost every breeze and every rain. The soil on mountain sides is washed 

 into the valleys, and in clayey countries, even on gentle slopes, great gullies are the 

 result of the destructive action of water unless the cover of vegetation is sufficient to 

 hold it in place. On the steep mountain sides of Europe, in order to prevent earth- 

 slides and destructive floods, protection-forests are fostered. In the case of a torrent, 

 the erosion begins in the little streamlets of the mountains — imperceptible at first, but 

 soon an immense volume of water descending on all sides into the channel course. 

 At first it is only loaded with silt ; but rocks, stones and timber soon accumulate in 

 the channel course. This powerful mass, by undermining the banks, receives constant 

 additions until the whole is dumped into the level plain, where the stream emerges 

 with diminished force. In many places, by persistent work the Swiss engineers and 

 foresters have prevented whole mountain sides from slipping and huge masses of rock 

 from crushing the villages in the valleys. Their boisterous streams, which are fed by 

 perpetual snow, must be constantly watched; and by walls of stone, wattle-work, and a 

 host of ingenious devices, they chain these forces until the trees which they have 

 planted can gain a footing that will hold the soil and rocks in place. The same 

 amount of water falls as ever, but the soil and debris which cause most of the mischief 

 are held firmly in place by the forest cover. 



In sandy soils, owing to their porosity, there is never any danger from the action 

 of water. This very looseness, however, which prevents the erosive action of water, 

 exposes the soil to the play of the wind unless it is held in place by the roots of plants. 



Along the shores of oceans and other large bodies of water, especially in the 

 region of the estuaries of large rivers, there are usually immense masses of shifting 

 sand. It is not within the scope of this paper to describe the formation of these sand- 

 banks. It is sufficient to say, therefore, that they usually begin as long sand-bars 

 behind which there are sheets of still water. These shallow bays in the course of time 

 fill up with mud, becoming salt marshes intersected by thoroughfares, salt ponds, and 

 winding creeks. In the meantime the long, flat sand-bars have developed into sea 

 islands, or beaches. When the tide falls, the sand of the shore, ground into powder 

 by the waves, and dried by the sun and wind, is blown in the direction of the pre- 

 vailing winds, usually inland. The sand moves like snow until it meets an obstruction, 

 when a dune, or sand-hill, forms, equal in height to the obstacle. A section through 

 a dune shows a beautiful stratification, the sand having been deposited in thin layers, 

 always varying, however, with the nature of the sand, the velocity of the wind, and 



