WATER-SUPPLY OF RIVERS. 291 



this, white poplar and white birch spring up, which, however, are liable 

 to be burned at any time, as the fire runs freely through all deciduous 

 timber in the spring, before the leaves are out, or during a very dry 

 time in summer. 



It is generally understood that the clearing away of the forests has 

 the effect of causing low water during the summer season, and the 

 reasons given for it are, the more rapid evaporation of water from the 

 soil, on account of the greater exposure to the sun in cleared than in 

 timbered land, and to this may be added the more rapid drainage, par- 

 ticularly in sandy soils, after the rotten logs, leaves, and other absorb- 

 ents, have been removed ; and it is also claimed that more rain falls 

 upon a section of country when it is timbered than after the land has 

 been cleared. The first of these reasons is undoubtedly correct, and 

 there is a great deal to show that the second is correct also, though I 

 do not think we know enough about the subject to justify us in stating, 

 as a scientific fact, that the amount of rainfall is affected by the growth 

 of timber. 



I have never known the existence of the spruce " duff " to be recog- 

 nized, as a fact of any importance, in governing our water-supply during 

 dry seasons ; but, unless I am greatly in error, it is a matter of the 

 greatest importance, and the destruction of the " duff," with the de- 

 struction of the forests, will prove as damaging to our streams as the 

 increased evaporation caused by the greater exposure of the land to 

 the sun. 



The waters from this immediate section of country flow into Lake 

 Champlain, and thence into the St. Lawrence River. The country 

 around the principal feeders of the Hudson River is almost identical 

 with the country described above^ and the same causes that affect the 

 water-supply of the Saranac and Ausable govern the water-supply of 

 the Hudson. 



The water-supply of the Hudson is a matter of very great importance 

 to the people of New York, and any facts tending to throw light upon 

 the natural laws governing it should be received with interest by the 

 intelligent people whose health, comfort, and prosperity, are partially 

 dependent upon the quantity and purity of the water in this noble river. 

 Hundreds of square miles of the country upon whose drainage the Hud- 

 son is dependent for its supply of water is covered with this " spruce- 

 duff," which, in the early spring, is a solid body of ice, holding untold 

 millions of gallons of the purest water, to be slowly thawed out and 

 given up to this river during the summer. In many places, and in most 

 seasons, part of this ice lasts through the whole summer ; in most places 

 it lasts well into the summer, and even after the ice is gone the "duff" 

 absorbs and stores away the rain, and, like a prudent housewife with 

 her confections, gives up her treasures in such a way as not to injure 

 the health of her children with her lavishness, nor exhaust her larder 

 before a fresh supply can reasonably be expected. 



