The 4th Flat Isle is about one mile long, and there is a smaller lying off its south-east end; they are a little elevated, and bear grass and small trees; but the shores are covered with mangroves, and surrounded with extensive flats of mud and sand.  The main coast, from which they lie two or three miles, is also low, with mangroves and shelving mud banks; but there is a deep channel between, of a mile in width.  In the evening, when the flood made, we steered into this channel with a light sea-breeze; but not having time to clear it before dark, the anchor was dropped in 4 fathoms at six o’clock.

My attention was attracted this evening by the vast extent of mud left dry on each side of the channel, and I ordered particular attention to be paid to the tides during the night.  At eleven o’clock, when the flood had ceased running, the depth was sounded and the lead line measured, and the same at half past five in the morning [SATURDAY 11 SEPTEMBER 1802] when it was low water; the difference was no less than thirty-two feet, and it wanted a day of being full moon; so that the springs may reach two or three feet higher.  The flood set S. by E., but its greatest rate did not exceed one mile and three quarters an hour.

At daylight the wind was south-east, directly against us.  We backed and filled, drifting up with the flood between the shoals on each side, and having the Lady Nelson and a boat ahead; but on approaching the end of the channel, our passage into the sound was blocked up by a bank running across, upon which there was not water enough for the ship by a fathom, and we therefore anchored.  At nine the tide had risen a fathom. and we passed over into the open sound; the depth immediately increasing to 4 and 7 fathoms, reduced to low water.  So long as the flood continued running we worked up the sound; and when it ceased, anchored three miles from a shallow opening in the low western shore, the second which had been observed.  We again proceeded upwards with the evening’s tide until dusk; and at nine next morning [SUNDAY 12 SEPTEMBER 1802] passed a fifth opening, and anchored abreast of the hilly projection on its east side, which I have named Upper Head, in 4 fathoms, soft bottom, two-thirds of a mile from the shore.  This was the first place on the main where there was any prospect of being able to land; for the western shore, thus far up, was equally low, and as much over-run with mangroves and defended by muddy flats, as the shores of Keppel Bay.

It being my intention to explore the head of Broad Sound with the brig and whale boat, a situation where tents could be fixed and an easy communication held with the ship during my absence, was the object now sought; and I immediately went with a party of the gentlemen, to ascertain how far Upper Head was calculated for our purpose.  We landed at half flood, without difficulty; and on ascending the hill, obtained a view of the Sound which exceeded my expectations.  Amongst the many bearings taken, were the following fixed points in the survey.