A mile and a half to the southward of Gun Island, opposite a singular-looking indentation in the outer side of the reefs, a small cluster of cliffy islets approaches within half a mile of them. It is rather singular that in another of the group--larger than Gun Island, lying in the centre of the lagoon, and the only one not visited by the Beagle's boats--water should have been found by a party who came from Swan River to save the wreck of a ship lost in 1843, close to the spot on which the Batavia struck more than two hundred years ago. This island is called in the chart Middle Island. The well is on the south point, and the water, which is very good, rises and falls with the tide. Doubtless this must have been the island on which the crew of Pelsart's ship found water, though for some time they were deterred from tasting it by observing its ebb and flow, from which they inferred it would prove salt. The north point of Gun Island, which our observations placed in latitude 28 degrees 53 minutes 10 seconds South, longitude 1 degree 53 minutes 35 seconds West of Swan River, is fronted for half a mile by a reef. MANGROVE ISLETS. The ship was now moved to the north-east extreme of the lagoon, to which we crossed in 17 fathoms--the depth we anchored in, a mile north-west from a cluster of islets covered in places with mangroves, from which they receive their name. To the southward the depth in the lagoon, as far as a square-looking island, was 15 and 16 fathoms. The north extreme of the south island lay three miles to the south east of the Mangrove Islets, by which we found that its length was nearly ten miles, with a general width of about a tenth of a mile. One of the eastern Mangrove Islets was a mere caY, formed of large flat pieces of dead coral, of the same kind as that of which I have before spoken as resembling a fan, strewed over a limestone foundation one foot above the level of the sea, in the greatest possible confusion, to the height of five feet. In walking over them they yielded a metallic sound. Pelsart, like Easter Group, is marked by a detached islet lying a mile off its north-east extreme. May 3. We fetched in under the Lee of Easter Group as the north-west gale of this morning commenced. The barometer did not indicate the approach of the gale, falling with it, and acting as in those we had encountered at Swan River. SINGULAR SUNSET. The sunset of the two days preceding had presented a very lurid appearance, and the most fantastically shaped clouds had been scattered over the red western sky. It seemed as though nature had determined to entertain us with a series of dissolving views. Headlands and mountains with cloud-capped pinnacles appeared and faded away; ships under sail floated across the sky; towers and palaces reared their forms indistinctly amid the vapour, and then vanished, like the baseless fabric of a dream.