168 GEOLOGICAL SURVEY OF NEW JERSEY. 



and compared with those of long periods in such a way that the 

 differences due to comparison of periods not contemporaneous are 

 eliminated as far as possible. 



Plate XI shows the mean temperature for the year, and the 

 mean annual rain-fall. This may be compared with Plate III, 

 showing the distribution of forests. At first sight it appears as 

 if the regions of heavy rain-fall coincide with those of abundant 

 forests, while the deforested areas along the Delaware and in the 

 Raritan valley show a light rain-fall ; but on closer examination 

 we find that the rain-fall in the pine forests varies from about 52 

 inches at Toms River to less than 40 inches at Cape May, with- 

 out any corresponding change in forest conditions. The varia- 

 tion in the cleared belt of the Cretaceous formation along the 

 Delaware is nearly as much, or from about 42 inches at Salem 

 to over 50 inches in Monmouth county. In the same way the 

 rain-fall of the Kittatinny valley ranges from 40 inches to over 

 48 inches, the whole being deforested to about the same extent, 

 while the Passaic valley, having over 40 per cent, of forest, 

 appears to have as small a rain-fall as the Raritan valley, where 

 there is less than 5 per cent, of forests. A careful study of the 

 annual rain-fall indicates that topographic relief has an effect 

 entirely superior to that of the forests, and we are forced to the 

 conclusion that it is impossible to trace any effect either upon 

 rain-fall or temperature due to the distribution of the forests. 



The temperature seems to be influenced largely by the sea, 

 and to a still more marked extent by the elevation ; and study- 

 ing the rain-fall and temperature together it appears that the 

 storms which usually occur with easterly winds show a more 

 abundant precipitation as such winds approach or cross high 

 ground, and a lighter precipitation in the valleys west. 



Plate XII shows the summer temperature, and the mean rain- 

 fall from April to September inclusive, these being the growing 

 months for forests. This plate is made up with a view to ascer- 

 taining the influence of forests when they are in leaf. Here, 

 also, it is impossible to detect any difference in the distribution 

 of rain-fall which may be fairly attributed to forests. In general 

 the same peculiarities which we have pointed out in the annual 

 rain-fall are present here. There is the same wide variation in 

 rain-fall in belts of country having uniform forest conditions- 



