ling that there is an adjustment of a
delicate kind, and an inability to see how known causes could have
produced such an adjustment. I believe I have shown, however, that such
an adjustment is not only possible but inevitable, unless at some point
or other we deny the action of those simple laws which we have already
admitted to be but the expressions of existing facts.

_Adaptation brought about by General Laws._

It is difficult to find anything like parallel cases in inorganic
nature, but that of a river may perhaps illustrate the subject in some
degree. Let us suppose a person totally ignorant of Modern Geology to
study carefully a great River System. He finds in its lower part, a deep
broad channel filled to the brim, flowing slowly through a flat country
and carrying out to the sea a quantity of fine sediment. Higher up it
branches into a number of smaller channels, flowing alternately through
flat valleys and between high banks; sometimes he finds a deep rocky bed
with perpendicular walls, carrying the water through a chain of hills;
where the stream is narrow he finds it deep, where wide shallow. Further
up still, he comes to a mountainous region, with hundreds of streams and
rivulets, each with its tributary rills and gullies, collecting the
water from every square mile of surface, and every channel adapted to
the water that it has to carry. He finds that the bed of every branch,
and stream, and rivulet, has a steeper and steeper slope as it
approaches its sources, and is thus enabled to carry off the water from
heavy rains, and to bear away the stones and pebbles and gravel, that
would otherwise block up its course. In every part of this system he
would see exact adaptation of means to an end. He would say, that this
system of channels must have been designed, it answers its purpose so
effectually. Nothing but a mind could have so exactly adapted the slopes
of the channels, their capacity, and frequency, to the nature of the
soil and the quantity of the rainfall. Again, he would see special
adaptation to the wants of man, in broad quiet navigable rivers flowing
through fertile plains that support a large population, while the rocky
streams and mountain torrents, were confined to those sterile regions
suitable only for a small population of shepherds and herdsmen. He would
listen with incredulity to the Geologist, who assured him, that the
adaptation and adjustment he so admired was an inevitable result of t