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378
The Story of the Atlantic Telegraph
·
Henry M. Field
65
"The
dangerous
part
of
this
course
has
hitherto
been
supposed
to
be
the
sudden
dip
or
bank
which
occurs
off
the
west
coast
of
Ireland,
where
the
water
was
supposed
to
deepen
in
the
course
of
a
few
miles
from
about
three
hundred
fathoms
to
nearly
two
thousand.
Such
a
rapid
descent
has
naturally
been
regarded
with
alarm
by
telegraphic
engineers,
and
this
alarm
has
led
to
a
most
careful
sounding
survey
of
the
whole
supposed
bank
by
Captain
Dayman,
acting
under
the
instructions
of
the
Admiralty.
The
result
of
this
shows
that
the
supposed
precipitous
bank,
or
submarine
cliff,
is
a
gradual
slope
of
nearly
sixty
miles.
Over
this
long
slope
the
difference
between
its
greatest
height
and
greatest
depth
is
only
eighty-seven
hundred
and
sixty
feet;
so
that
the
average
incline
is,
in
round
numbers,
about
one
hundred
and
forty-five
feet
per
mile.
A
good
gradient
on
a
railway
is
now
generally
considered
to
be
one
in
one
hundred
feet,
or
about
fifty-three
in
a
mile;
so
that
the
incline
on
this
supposed
bank
is
only
about
three
times
that
of
an
ordinary
railway.
In
fact,
as
far
as
soundings
can
demonstrate
any
thing,
there
are
few
slopes
in
the
bed
of
the
Atlantic
as
steep
as
that
of
Holborn
Hill.
In
no
part
is
the
bottom
rocky,
and
with
the
exception
of
a
few
miles,
which
are
shingly,
only
ooze,
mud,
or
sand
is
to
be
found."
[C]
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