LXXI.] 



OF SELBORNE. 



201 



moisture ; and so render those districts habitable by condensa- 

 tion alone. 



Trees in leaf have such a vast proportion more of surface than 

 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 

 condense very fast ; and besides, evergreens 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 advan- 

 tageous some trees are in preference to others. 



Trees perspire profusely, condense largely, and check eva- 

 poration 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. 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 

 districts will allow that they ever saw springs in such a soil, but 

 only 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 



Vide Kalni's Travels in North America. 

 VOL. I. 1) I) 



