PERENNIAL PONDS. 189 



those that are naked, that, in theory, their condensations should 

 greatly exceed those that are stripped of their leaves ; but, as the 

 former imbibe also a great quantity of moisture, it is difficult to 

 say which drip most : but this I know, that deciduous trees that 

 are entwined with much ivy seem to distil the greatest quantity. 

 Ivy-leaves are smooth, and thick, and cold, and therefore con- 

 dense very fast ; and besides ever-greens imbibe very little. 

 These facts may furnish the intelligent with hints concerning 

 what sorts of trees they 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 largely, and check evapora- 

 tion 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 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 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 con- 

 taining 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 over- hung 

 with two moderate beeches, that, doubtless, at tunes afford it 



* Vide Kalnr's Travels to North-America. 



