We were on the top of the northern Slate Island early; a small islet with a reef off its northern extreme, bore north a mile and a half, and a low sandy isle, West 1/4 North about 15 miles; this was a most unwelcome discovery, as it lay in the track of vessels approaching Brecknock Harbour, and which Captain King must have passed very close to in the night without being aware of it. We were fortunate in being able to intersect our lines to the extremes of all the islands forming the north side of Camden Sound from this station, which rendered it one of great importance. Of the interior we saw even less than from Point Hall, and the prospect if possible was more cheerless. Our again meeting rocks of transition origin, led us to infer that the soil in the neighbourhood was of a better quality, as the decomposition of rocks of this class furnishes a much more fertile soil than sandstone of recent formation. Leaving the Slate Islands, we reached Entrance Isle, in Brecknock Harbour, in time to secure observations for the rates of the chronometers, which we found had been performing admirably; they placed the sandy bay on the east side of Entrance Isle, in longitude 124 degrees 30 minutes East; the latitude as before given, 15 degrees 27 1/4 minutes South. FERTILE COUNTRY. At this place Mr. Helpman rejoined us, having completed the examination of the south shore of the harbour; from a high hill over it he discovered some fine country, bearing East-South-East about eight miles. In speaking of it, he says, "I was invited to the top of this hill by the certainty of a good view of the interior over the low land forming the south-eastern shore of the harbour, and most amply was I repaid for the toil of ascending it, by feasting my eyes on a most luxuriant well-watered country, lying at the eastern foot of a remarkable peak, visible from Port George the Fourth. To the North-East there lay a range of hills,* apparently of no great elevation. (*Footnote. Macdonald Range of Lieutenant Grey, considered by him 1400 feet high.) BRECKNOCK HARBOUR. Part of this rich land extended to within five miles of the south-eastern part of Brecknock Harbour." The proximity of such fertile land to this fine port was of great importance, and induced us to consider it a great addition to our discoveries in north-western Australia. Under this impression, I trust the following brief description of it may not be without its value in the eyes of some of my readers. Brecknock Harbour is six miles deep, extending gradually from a width of one and three quarter miles at the entrance to five at the head, and has a depth of water varying from five to seven fathoms, with a soft muddy bottom. The few observations on the tides our short visit afforded, make the time of high-water, on full and change day, about half an hour before noon, when the rise is nearly thirty feet, and the strength of stream in the entrance nearly two knots. LIEUTENANT GREY. April 16.