OF SELBORNE. 299 



wish to be perennial: and show them how advantageous 

 some trees are in preference to others. 



Trees perspire profusely, condense largely, and check 

 evaporation so much, that woods are always moist : no 

 wonder therefore 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 bodies of water are much diminished ; so 

 that some streams, that were very considerable a cen- 

 tury ago, will not now drive a common mill 1 . Besides, 

 most woodlands, forests, and chases, with us, abound 

 with pools and morasses ; no doubt, for the reason 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 

 droughts of summer. On chalk-hills I say, because in 

 many rocky and gravelly soils, springs usually break 

 out pretty high on the sides of elevated grounds and 

 mountains ; but no person acquainted with chalky dis- 

 tricts will allow that they ever saw springs in such a 

 soil, but in valleys and bottoms, since the waters of so 

 pervious a stratum as chalk all lie on one dead level, 

 as well-diggers have assured me again and again. 



Now, we have many such little round ponds in this 

 district; and one in particular on our sheep-down, 

 three hundred feet above my house; which, though 

 never above three feet deep in the middle, and not more 

 than thirty feet in diameter, and containing perhaps not 

 more than two or three hundred hogsheads of water, 

 yet never is known to fail, though it affords drink for 

 three hundred or four hundred sheep, and for at least 

 twenty head of large cattle beside. This pond, it is true, 

 is overhung with two moderate beeches, that, doubtless, 



1 Vide Kalm's Travels to North America. 



