OF SELBORNE. 225 
know, that deciduous trees that are entwined with much ivy 
seem to distil the greatest qua^ntity. 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.^ 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 again 
and again. 
"Now, we have many such little roimd 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 
Vide Kalm's " Travels to North America." — G. W. 
Q 
