144 EFFECTS OF FORESTS ON MOISTURE. 



It is remarked by Marsh, that " it has long been a popularly settled 

 belief that vegetation and the condensation and fall of atmospheric 

 moisture are reciprocally necessary to each other, and even the poet 

 sings of 



Afrio's barren aand, 

 Where nought can grow, because it raineth not, 

 And where no rain can fall to bless the land, 

 Because nought grows there." * 



Here we have an illustration of the converse fact : one measure of 

 humidity promoting vegetation, and vegetation not only arresting the 

 desiccation but so reversing the process that an increased humidity 

 is the consequence. 



Sect IV. — Oases, Illustrative of Effects of Forests on Humidity, 

 correspondinng to such as have been adduced. 



Besides the cases which have been brought forward as indicative of 

 the effects of forests upon the humidity of a country, there are others 

 which point to the same conclusion, which may be adduced, not as 

 corroborative testimony, but as independent facts, which are in 

 accordance with what has been alleged. Continuing observations 

 made on the Islands and Continent of Africa, I cite first the case of 

 Madeira. 



Madeira does not, like St. Helena and Ascension, supply evidence 

 of a restored or newly produced humidity following the planting of 

 treesj but it supplies testimony to the effects of trees on the humiditty 

 of the atmosphere and soil, which is of importance. 



Washington Irving, in his "History of Columbus," refers to an 

 ancient document which is believed to have been drawn up by one of 

 the first discoverers of Madeira, about the year 1378. According to 

 this document, — " The country was delightful. The forests were 

 stately and magnificent. There were trees laden with excellent 

 fruits. The waters were cool and limpid. On penetrating a little 

 distance they found a beautiful sheltered meadow, the green bosom 

 of which was bordered by laurels and refreshed by a mountain stream, 

 whiah ran sparkling over pebbles." 



In accordance with this statement is the following glowing descrip- 



* " Det golds Striig i Afrika. 



Der Intet voxe kan, da ei det regner, 

 Ogj omvendt, ingen Regu kau falde, da 

 Der Intet Toxer," 

 Faltidak-Muillek, Adam Homo, ii, 408. 



