122 MAN SPECIALLY DESTRUCTIVE TO AQUATIC ANIMALS. 
European species, which, is familiar to every one acquainted 
with both continents, is probably due less to specific difference 
than to the fact that, even in the parts of the blew World. 
which have been longest cultivated, wild nature is not yet 
tamed down to the character it has assumed in the Old, and 
' 
which it wfill acquire in America also when her civilization 
shall be as ancient as is now that of Europe. 
Man has hitherto hardly anywhere produced such climatic 
or other changes as would suffice of themselves totally to banish 
the wild inhabitants of the dry land, and the disappearance of 
the native birds and quadrupeds from particular localities is to 
be ascribed quite as much to his direct persecutions as to the 
want of forest shelter, of appropriate food, or of other conditions 
indispensable to their existence. But almost all the processes 
of agriculture, and of mechanical and chemical industry, are 
fatally destructive to aquatic animals within reach of their 
influence. When, in consequence of clearing the woods, the 
changes already described as thereby produced in the beds 
and currents of rivers, are in progress, the spawning grounds 
of fish are exposed from year to year to a succession of me¬ 
chanical disturbances ; the temperature of the water is higher 
in summer, colder in winter, than when it was shaded and 
protected by wood; the smaller organisms, which formed the 
sustenance of the young fry, disappear or are reduced in num¬ 
bers, and new enemies are added to the old foes that preyed 
upon them; the increased turbidness of the water in the 
annual inundations chokes the fish; and, finally, the quick¬ 
ened velocity of its current sweeps them down into the larger 
rivers or into the sea, before they are yet strong enough to 
support so great a change of circumstances.* Industrial oper- 
* A fact mentioned by Schubert—and which in its causes and many of 
its results corresponds almost precisely with those connected with the 
escape of Barton Pond in Vermont, so well known to geological students— 
is important, as showing that the diminution of the fish in rivers exposed 
to inundations is chiefly to be ascribed to the mechanical action of the 
current, and not mainly, as some have supposed, to changes of temperature 
occasioned by clearing. Our author states that, in 1796, a terrible inun- 
