Fathom lines, a caution. - Except in plans of harbours that have been surveyed in detail, the five fathom line on most Admiralty charts is to
be considered as a caution or danger line against unneccessarily approaching the shore or bank within that line, on account of the
possibility of the existence of undiscovered inequalities of the bottom, which nothing but an elaborate detailed survey could reveal. In general
surveys of coasts or of little frequented anchorages, the necessities of navigation do not demand the great expenditure of time required for
such a detailed survey. It is not contemplated that ships will approach shores in such localities without taking special precautions.
The ten fathom line is, on rocky shores, as before mentioned, another warning, especially for ships of heavy draught.
Charts where no fathom lines are marked must be especially regarded with caution, as it generally means that soundings were too scanty and
the bottom too uneven to enable them to be drawn with accuracy.
Isolated soundings, shoaler than surrounding depths, should always be avoided, especially if ringed round, as there is no knowing how closely
the spot may have been examined.