.348 NATURAL HISTORY 



should plant round small ponds that they 

 would wish to be perennial : and show 

 them how advantageous some trees are in 

 preference to others. 



Trees perspire profusely, condense large- 

 ly, and check evaporation so much, that 

 woods are always moist : no wonder there- 

 fore that they contribute much to pools 

 and streams. 



That trees are great promoters of lakes 

 and rivers appears from a well-known fact 

 in North- America ; for, since the woods and 

 forests have been grubbed and cleared, all 

 })odies of water are much diminished ; so 

 that some streams, that were very consi- 

 derable a century ago, will not now drive a 

 common mill.* Besides, most woodlands, 

 forests, and chases, with us abound with 

 pools and morasses ; no doubt for the rea- 

 son given above. 



To a thinking mind few phenomena are 

 more strange than the state of little ponds 

 on the summits of chalk-hills, many of 

 which are never dry in the most trying 



* Vide Kabn's Travels to North-Amerka. 



