150 NATURAL SELECTION VII 
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 herds- 
men. He would listen with incredulity to the geologist who 
assured him that the adaptation and adjustment he so admired 
was an inevitable result of the action of general laws; that 
the rains and rivers, aided by subterranean forces, had 
modelled the country, had formed the hills and valleys, had 
scooped out the river beds and levelled the plains; and it 
would only be after much patient observation and study, 
after having watched the minute changes produced year by 
year, and multiplying them by thousands and ten thousands, 
—after visiting the various regions of the earth and seeing the 
changes everywhere going on, and the unmistakable signs of 
greater changes in past times,—that he could be made to 
understand that the surface of the earth, however beautiful 
and harmonious it may appear, is strictly due in every detail 
to the action of forces which are demonstrably self-adjusting. 
Moreover, when he had sufficiently extended his inquiries, 
he would find that every evil effect which he would imagine 
must be the result of non-adjustment does somewhere or other 
occur, only it is not always evil. Looking on a fertile valley, 
he would perhaps say: “If the channel of this river were not 
well adjusted—if for a few miles it sloped the wrong way— 
the water could not escape, and all this luxuriant valley, full of 
human beings, would become a waste of waters.” Well, there 
are hundreds of such cases. Every lake is a valley “ wasted 
by water,” and in some cases (as the Dead Sea) it is a positive 
evil, a blot upon the harmony and adaptation of the surface 
of the earth. Again, he might say—‘“TIf rain did not fall 
here, but the clouds passed over us to some other regions, 
this verdant and highly cultivated plain would become a 
desert.” And there are such deserts over large portions of 
the earth, which abundant rains would convert into pleasant 
dwelling-places for man. Or he might observe some great 
