THE VALUE OF OUR FORESTS. 179 



drying muddy roads as being greater than that of sunshine, while we 

 fail to recognize the fact that the desiccating effect is the same upon 

 the fields as upon the roads. 



Forests have a very obvious influence also in preventing the occur- 

 rence of floods and droughts. When the rains fall upon the open, 

 un wooded country, unless it is of a quite level character, they flow 

 off at once into the beds of the neighboring streams, and pour their 

 united flood into the larger rivers, swelling their volume rapidly to 

 such an extent that their waters can not be confined within their 

 banks, but break out and overspread the adjacent lands, carrying de- 

 struction oftentimes to the growing crops, covering fertile fields with 

 masses of gravel and rubbish of various sorts, interfering with manu- 

 facturing interests, and often destroying life itself. These floods are 

 succeeded by periods of drought. The flow of water in the streams 

 shrinks away, often leaving their beds almost dry. As a consequence, 

 crops and herds suffer, the mill-wheels are stopped or turn but slowly 

 and feebly, the transportation of merchandise is impeded, and the va- 

 rious industries of life suffer. The forests prevent such a deplorable 

 condition of things. The spongy soil formed by their fallen leaves, 

 accumulated for years, retains the rain which falls upon it as in a great 

 reservoir, and obliges it to flow off gradually instead of with a sudden 

 flood. The difference in the operation in the two cases may be likened 

 to that between the flow of the rain from a smoothly shingled house- 

 roof and from one covered with thatch. In the one case the water 

 runs at once to the ground without any impediment. In the other it 

 sinks into the straw to a considerable depth and trickles thence for 

 days perhaps after the rain has ceased to fall. So, our hillsides and 

 mountain-slopes, where the forests are most usually found, are the 

 world's great roofs or water-sheds, from which, if they are thatched 

 with trees, the water flows off slowly and in the most desirable man- 

 ner into the streams and upon the lands of the regions below, but, 

 if stripped of this protecting covering, then with sudden and disastrous 

 flood which no art of man can withstand. 



This is well illustrated by the report of the effect of a storm in 

 two neighboring ravines in the valley of the Durance in southeastern 

 France, the Ravine de St. Phalez and the Ravine de la Combe d'Yeuse. 

 St. Phalez runs north and south, has a basin of reception fifty hectares 

 (one hundred and twenty-five acres) in extent, is well cultivated and 

 has an argillaceous soil. Combe d'Yeuse is much more steep, has a 

 basin of reception of two hundred and fifty hectares (seven hundred 

 and twenty-five acres), and is covered with pines and oaks. In other 

 respects the two ravines are alike. 



In September, 1864, an abundant rainfall took place. On the 

 morning after the rain the ravine of St. Phalez was flowing with a 

 small stream. The Combe d'Yeuse was dry. During the day a water- 

 spout struck the mountain and prevailed for not more than forty min- 



