From the summit of this island a set of bearings was obtained, particularly of the islands to the northward and westward. The ascent, on account of its steep and rugged nature, was very difficult and even dangerous, for the stones were so loose and decomposed that no solid footing could be found. The top of the rock is covered with a thick brush of Acacia leucophoea (of Lacrosse Island) many trees of which were obliged to be cut down or cleared away before the various objects could be seen from the theodolite. Mr. Cunningham collected here specimens of eighteen different sorts of plants. Bat Island is a mass of sandstone superincumbent upon a quartzose basis and intersected by nearly vertical veins of white quartz, the surface of which was in a crystallized state. The floor of the cavern was covered with heaps of water-worn fragments of quartzose rock, containing copper pyrites, in some of which the cavities were covered by a deposit of greenish calcedony. The sides of the cavern had a stalagmitical appearance but the recess was so dark that we could not ascertain either its formation or extent; it did not however appear to be more than twelve or fourteen yards deep. On first entering it we were nearly overpowered by a strong sulphureous smell which was soon accounted for by the flight of an incredible number of small bats which were roosting in the bottom of the cave and had been disturbed by our approach. We attempted to grope our way to the bottom, but, not having a light, were soon obliged to give up its further examination. The island is connected to the cape by a narrow ridge of rocks which the spring-tides may probably cover. The main corresponds with the island in character and general conformation, being extremely barren and rocky, and of the same description of sandstone, the strata of which appear nearly horizontal; the greatest deviation from that position not being more than an inclination of 5 degrees to the south-east.