1 64 GEOLOGICAL SURVEY OF NEW JERSEY. 



1,360 horse-power, the value of which, at a rental of $35 per 

 horse-power per annum, would be $47,600, or the interest at 5 

 per cent, on $952,000. 



We do not advance these figures as exact measures of the 

 value of forests, but they may be taken as indicative of the 

 possible financial loss which might result in stream-flow alone 

 from deforesting such of our water-sheds as are not adapted for 

 cultivation. 



It will also be seen how amply this effect of forests in increas- 

 ing the stream-flow for five or six months, during the latter part 

 of a dry period, explains popular opinion as to a falling-off of 

 streams when the forests are cut off. Such an effect is very 

 much more likely to impress itself upon the popular mind than 

 an increase of evaporation, which would tend to decrease the 

 total run-off for the year without being very apparent to ordinary 

 observation. Being a much more enduring effect, it would also 

 be more noticeable than any change in the greatest or least rate 

 of discharge. 



We may illustrate the effect of the great absorptive capacity 

 of forests in diminishing floods by comparing the run-off of the 

 forested Passaic and deforested Raritan during the dry period in 

 1892, during which period both streams were being measured. 

 This run-off,, together with the rain-fall month by month, is 

 shown in the following table : 



, Passaic. , Raritan. . 



1892. Rain. Run off. Rain. Run-off. 



June 468 1.20 4.06 i 60 



July, ... 3.27 .52 4.11 .57 



August, 4.39 .53 3 61 .47 



September, ... 2.17 .40 275 .31 



October 72 .25 .32 .24 



November, ....'.,..... 684 138 6.99 218 



It will be seen the rain-fall conditions were very similar ; 

 during the dry months, from July to October, inclusive, the run- 

 off on the Passaic was 1.70 inches, and on the Raritan 1.59 

 inches. While the run-off before August was greater on the 

 Raritan, during the following three months it declined to a con- 

 siderably lower point. During November rains were abundant 

 on both catchments, and of these rains 1.38 inches ran off on 

 the Passaic, and 2.18 inches, or nearly 60 per cent, more, on the 



