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 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 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 chalk 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 containing 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 overhung
with two moderate beeches, that, doubtless,