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210
The Fairy-Land of Science
·
Arabella B. Buckley
97
There
are
two
things
in
particular
to
notice
in
a
waterfall
like
this.
First,
how
the
water
and
spray
dash
against
the
bottom
of
the
cliff
down
which
it
falls,
and
grind
the
small
pebbles
against
the
rock.
In
this
way
the
bottom
of
the
cliff
is
undermined,
and
so
great
pieces
tumble
down
from
time
to
time,
and
keep
the
fall
upright
instead
of
its
being
sloped
away
at
the
top,
and
becoming
a
mere
steam.
Secondly,
you
may
often
see
curious
cup-shaped
holes,
called
"pot-holes,"
in
the
rocks
on
the
sides
of
a
waterfall,
and
these
also
are
concerned
in
its
formation.
In
these
holes
you
will
generally
find
two
or
three
small
pebbles,
and
you
have
here
a
beautiful
example
of
how
water
uses
stones
to
grind
away
the
face
of
the
earth.
These
holes
are
made
entirely
by
the
falling
water
eddying
round
and
round
in
a
small
hollow
of
the
rock,
and
grinding
the
pebbles
which
it
has
brought
down,
against
the
bottom
and
sides
of
this
hollow,
just
as
you
grind
round
a
pestle
in
a
mortar.
By
degrees
the
hole
grows
deeper
and
deeper
and
though
the
first
pebbles
are
probably
ground
down
to
powder,
others
fall
in,
and
so
in
time
there
is
a
great
hole
perforated
right
through,
helping
to
make
the
rock
break
and
fall
away.
In
this
and
other
ways
the
water
works
its
way
back
in
a
surprising
manner.
The
Isle
of
Wight
gives
us
some
good
instances
of
this;
Alum
Bay
Chine
and
the
celebrated
Blackgang
Chine
have
been
entirely
cut
out
by
waterfalls.
But
the
best
know
and
most
remarkable
example
is
the
Niagara
Falls,
in
America.
Here,
the
River
Niagara
first
wanders
through
a
flat
country,
and
then
reaches
the
great
Lake
Erie
in
a
hollow
of
the
plain.
After
that,
it
flows
gently
down
for
about
fifteen
miles,
and
then
the
slope
becomes
greater
and
it
rushes
on
to
the
Falls
of
Niagara.
These
falls
are
not
nearly
so
high
as
many
people
imagine,
being
only
165
feet,
or
about
half
the
height
of
St.
Paul's
Cathedral,
but
they
are
2700
feet
or
nearly
half-a-mile
wide,
and
no
less
than
670,000
tons
of
water
fall
over
them
every
minute,
making
magnificent
clouds
of
spray.
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