260 RELATION OF POEEBTS TO 



fall. That even a much lower ridge than the Andes may intercept 

 the whole moisture of the atmosphere is proved by a well-known 

 phenomenon in India, when the Ghauts, a chain only 3000 or 4000 

 feet high, divide summer from winter, as it is called: that is, they 

 have copious rains on their windward side, while on the other the 

 weather remains clear and dry ; and the rains regularly change from 

 the west side to the east with the monsoons. 



" In the region beyond the 30th parallel this effect will be reversed. 

 The Andes will in this case serve as a screen to intercept the moisture 

 brought by the prevailing west winds from the Pacific Ocean ; rains 

 will be copious on their summits, and in Chili on the their western 

 declivities, but none will fall on the plains to the eastward, except 

 occasionally when the winds blow from the Atlantic." 



And he adds, — " The views on the subject of climate we have been 

 unfolding will enable us to throw some light on an interesting point, 

 the distribution of forests." 



There is appended a small map of America, in which by long 

 hatched lines are shown the positions of the chains of mountains ; 

 white spaces represent lands on which little or no wood grows ; 

 shading represent the regions of forests, dense forests being repre- 

 sented by double shading, and thinner ones by open lines ; while 

 arrows indicate the direction of prevailing winds. And in explanation 

 it is stated, — ^"In speaking of the region, of forests, we neither restrict 

 the term to those districts where the natural woods present an un- 

 broken continuity, nor extend it to every place where a few trees 

 grow in open plains. It is not easy to give a definition that will be 

 always appropriate ; but in using the expression we wish to be under- 

 stood as applying it to ground where the natural woods cover more 

 than one-fourth of the surface." And there is given the following 

 statement in regard to the distribution of the forests, — " In North 

 America, to the west of the Eocky mountains, is thus represented a 

 woody region, extending from lat. 35° to about 58°, of unknown 

 breadth, densely wooded from the coast, more thinly wooded towards 

 the mountain range ; to the east of the mountains,' an extensive 

 region stretching E.NE. to the ocean, partly a bare desert, partly 

 covered with grass and clothed with trees. On the east coast and 

 more to the south is the Allegany range, with dense forests on the 

 east and the south and thin on the west, the forest region thus 

 indicated being bounded by a curved line passing from the mouth of 

 the St. Lawrence, in lat. 50°, through Lake Huron to St. Luis in 

 Mexico ; and an arrow points out the direction of the wind turned 



