OF SELBORNE. 225 



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 

 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 watei 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 mo- 

 rasses, 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 agnin 

 and again. 



Now, we have many such little round ponds in this dis- 

 trict; and one in particular on our sheep-down, 300 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 



1 Vide Kalm's " Travels to North America." G. W. 

 Q 



