412 FORESTS AND THEIR CLIMATIC INFLUENCE. 



the trees had not taken place. The influence of woods in cooling the 

 air is not as great, therefore, as has been supposed. The state of the 

 soil, moreover, singularly modifies that influence. 



EFFECTS OF THE CLEARING AWAY OF FORESTS ON SPRINGS AND 



WATER-COURSES. 



The effects of disboscation on the sources and quantities of living 

 water which irrigate a country are of most important consideration, and 

 heuce require serious attention. Tlie dilliculty in verifying these effects 

 is the greater inasmuch as it is impossible to say, a priori, whether a 

 forest or portion of a forest, destined to be cleared away, contributes to 

 supply such or such a source, such or such a river. Springs are owing, 

 in general, to the infiltrations of rain-water in a pervious formation, 

 through which this water siuks until it meets with au impervious stra- 

 tum, flowing over the latter when it is in an inclined position, and event- 

 ually rising in streams or fountains. The water of wells has the same 

 origin. Large springs are ordinarily found in mountainous regions. 



Forests also contribute to the formation of springs, not only by reason 

 of the humidity which they produce, and the obstacles which they op- 

 pose to the evaporation of the water which falls on the surface, but fur- 

 ther because of the roots of the trees, which, by dividing the soil, render 

 it more pervious and thus facilitate infiltration. A great number of 

 illustrative examples have been cited, but we shall here adduce only a 

 few which may be regarded as among the most remarkable. 



Strabo informs us that it was necessary to take great precautions to 

 l)revent the country of Babylonia from being submerged. The Eu- 

 l)hrates, which begins to swell, he tells us, at the close of spring, when the 

 snows melt on the mountains of Armenia, overflows at the beginning of 

 summer, and would necessarilj^ form vast accumulations of water on the 

 cultivated lands were not the superflus turned aside by means of trenches 

 and canals. This state of things exists no longer. M. Oppert, who 

 some years ago traveled through Babylonia, reports that the volume of 

 water conveyed by the Euphrates is much less than in past ages, that 

 inundations no longer occur, that the canals are dr^-, the marshes ex- 

 hausted by the great heats of summer, and that the country has ceased 

 to be insalubrious. This retreat of the waters can only be attributed, 

 as he found means to satisfy himself, to the clearing away of the forests 

 on the mountains of Armenia. 



The efifecrs in question, though denied by some, are not the less in- 

 contestible, as is shown by examples which I proceed to report and 

 which rest upon observations worthy of entire confidence. 



De Saussure {Voyage dans les Alpes, t. ii,ch. 16) long ago pointed out 

 the diminution of water in the lakes of Switzerland, especially in Lakes 

 Morat, Keufchatel, and Bienne, as a consequence of the clearing away 

 of the forests. Choiseul Gouflier was not able to distinguish in the Troad 

 the Eiver Scamander, which was still navigable in the time of Pliny. 

 Its bed is now entirely dry ; but the cedars also, which covered Mount 

 Ida, whence it took its source, as well as the Simois, exist no longer. 



M. Boussingault, {Annales de CJtimie et dc Phydque, t. xiv, p. 113,) 

 who studied this subject during his sojourn in Bolivia, selected as the 

 subject of his observations the lakes situated in the plains or on difler- 

 ent steps of the mountains. The valley of xVragua, pro^iuce of Vene- 

 zuela, situated at a short distance from the coast, has a very favorable 

 climate, and is of great fertility. It is closed in on every side, the rivers 

 which traverse it having no issue toward the ocean ; by their union 



