124 PHYSICAL GEOGRAPHY. 



are facts that show that forests have a great influence on the climate,— if 

 not on the annual rain-fall, yet on its distribution during the months of 

 the year and the hours of the day. 



In the central and southern portion of New Hampshire, the hay crop 

 is frequently cut short by drouth, while in the northern portion of the 

 state, often the same year, the hay crop is above the average; yet the 

 annual rain-fall is less in the northern than either in the central or 

 southern part of the state. But in the north there are abundant forests ; 

 and the rain is distributed through the months when it is needed for the 

 crops to grow and mature. The effect of the diminution and increase of 

 vegetation is shown in the well known facts in regard to Lake Tacarigua, 

 Venezuela During the last thirty years of the past century, it was found 

 to be gradually drying up ; but when the valley of Aragua was devastated 

 by war, the country, by the rapid growth of vegetation, was soon covered 

 with forests ; and it was observed by Boussingault that the water of the 

 lake had risen so that it covered much of the country that was formerly 

 cultivated. 



The gradual rise in the height of the water of the Great Salt lake, in 

 Utah, at the rate nearly of a foot per year, and the gradual increase in 

 rain-fall more than three inches per year since the country has been cul- 

 tivated, — and there has been a great increase of vegetation on account of 

 irrigation, — is an important example, as showing the effect of the increase 

 of vegetation.* 



The preservation of the vegetation on our mountains is of great 

 importance, not only in modifying the distribution of rain, but also in 

 moderating the extremes of cold in winter. 



Our mountains, especially the higher summits, except where it has been 

 destroyed by fire, are covered to a considerable depth by peat formed 

 chiefly from moss and lichens. Now it has been found by experiment 

 "that peat moss can absorb more than twice its own weight of water, dry 

 clay nearly its own weight, dry earth, or garden mould, more than half its 

 own weight, and dry sand a little more than a third of its own weight. 

 With equal times of drying, under the same circumstances, peat moss lost 

 two thirds of all the water it contained, clay and earth more than three 



* Monthly Reports of the Department of Agriculture. 



