OF SELBORNE. 237 
very little. These facts may furnish the intelligent 
with hints concerning what sort 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 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 water are 
much diminished ; so that some streams, that were 
very considerable a century ago, will not now drive 
acommon mill.* Besides, most woodlands, forests, 
and chases with us abound with pools and morass- 
es, no doubt for the reason given above. 
To a thinking mind, few phenomena are more 
strange than the state of little ponds on the sum- 
mits of chalk-hills, many of which are never dry 
in the most trying droughts of summer. On chalk. 
hills, | say, because in many rocky and gravelly 
soils springs usually break out pretty high on the 
sides of elevated grounds and mountains; but no 
persons 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 pervi- 
ous 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, 
* Vide Kalm’s Travels in North America. 
