200 NA TURA L HIST OR Y OF SEL BORNE. 



forests have been grubbed and cleared, all bodies of water are much 

 diminished; so that some streams, that were very considerable 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 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 districts will 

 allow that they ever saw springs in such a soil but in valley 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, at times afford it much supply : but then we have others 

 as small tfiat, without the aid of trees, and in spite of evaporation 

 from sun and wind, and perpetual consumption by cattle, yet con- 

 stantly maintain a moderate share of water, without overflowing in 

 the wettest seasons, as they would do if supplied by springs. By 

 my journal of May, 1775, it appears that "the small and even con- 

 siderable ponds in the vales are now dried up, while the small ponds 

 on the very tops of hills are but little affected.'' Can this difference 

 be accounted for from evaporation alone, which certainly is more 

 prevalent in bottoms ? or rather have not those elevated pools some 

 unnoticed recruits, which in the night time counterbalance the 

 waste of the day ; without which the cattle alone must soon exhaust 

 them ? And here it will be necessary to enter more minutely into 

 the cause. Dr. Hales, in his Vegetable Statics, advances, from ex- 

 periment, that "the moister the earth is the more dew falls on it in 

 a night ; and more than a double quantity of dew falls on a surface 

 of water than there does on an equal surface of moist earth." Hence 



* Vide Kalm's Travels to North America. 



