the barrier, the sea appears to be generally
unfathomable; but within, and amongst the reefs, there are soundings
every where. Nor is the depth very unequal, where the bottom is sandy;
but like the breadth of the reefs and the arm they inclose, it diminishes
as we advance northward, from 60 to 48, to 35, and to 30 fathoms near our
opening; and to 20 at Cape Tribulation. The further to leeward, the
shallower the water, seems to be a law amongst coral reefs.

There is some variation in the tide in different parts of the barrier,
but the most general rise is about two fathoms; abreast of the
Northumberland Islands, however, where the flood from the south-east seems
to meet that from the northward, it is three fathoms, and perhaps more.
The time of high water there, and also at the eastern Cumberland Islands,
is _eleven hours after_ the moon's passage; but it probably accelerates
north-westward, to the opening, and then retards further on: at Endeavour
River, captain Cook found it to be high water an hour and a half earlier
than is above given.

It has been said, that the width of the opening by which we got out to
sea, is uncertain; it is undoubtedly four, and possibly more leagues, but
there are many small, unconnected banks in it. To a ship desiring access
to any part of the coast, south of Endeavour River, I should certainly
recommend her to enter the inclosed sea by the way of Break-sea Spit, if
able to choose her own route; but the question is, whether a ship driven
by stress of weather, or by accident, to seek the coast, might steer for
the opening with a fair prospect of passing through in safety? I
certainly think she might; with the precaution of not attempting the
passage late in the day. The marks to be given for it, are, the latitude
18 deg. 52', longitude 148 deg. 2', variation 6 deg. east with the ship's head north
or south, and the soundings. When right off the opening, bottom will be
found at from 70 to 40 fathoms before any reefs come in sight; whereas,
if breakers be seen and no soundings can be obtained, it may be certainly
concluded that the ship is not in the fair way for this opening, and
probably, that no large opening exists in that part of the barrier. On
getting soundings and afterwards making the reefs near the situation
above given, a ship should push through the first opening of two miles
wide that presents itself, and steer south-westward amongst the inner
reefs for the land; and it will not b