Mans Hat. Stone cairn (Site IIIA3) A sandstone cairn stands adjacent to the 2nd Class Passenger Accommodation building P12. Built during the late 1830s, this is the sole remaining cairn of a line of thirteen which denoted the early boundary of the quarantine ground. It is in good condition. This cairn is the earliest surviving in situ structure associated with the place's quarantine function and demonstrates the early need for isolation and security. Natural heritage Overview and description The study area for the natural heritage plan specifically requires consideration of the water body and the sea bed between Cannae Point and Spring Cove, including Quarantine Beach and store Beach; the Third Quarantine Cemetery within the former Defence land at North Head, and associated installations. The natural heritage items are those items recorded as occurring in the subject study area, or those items with a high probability of occurring within the area, based on studies, surveys and reports of the flora and fauna on North Head generally. Native bushland in the North Head Defence property and other parts of the North Head component of Sydney Harbour National Park is contiguous with bushland within the study area and fauna may move from one area to another. Some fauna may occur sporadically or seasonally in different parts of North Head, and others such as raptors have territories which span large areas regardless of roads, walls or fences. Therefore, some of the conservation significance of the study area is linked to the wider context of North Head as a whole and even beyond. For example, the significance of the Little Penguin colony is considered in the context of other colonies and the feeding range of individual birds. The maintenance of genetic diversity within plant communities is aided by free movement of bird, mammal and insect pollinators. Wind-borne pollen is dispersed widely; however maximum distances between plants which still allow effective pollination are seldom studied and, in consequence, little understood. It is axiomatic that larger units of vegetation enhance the prospects of long-term survival of genetic diversity in remnant plant communities. Thus the biodiversity values of plants and animals in the study area are discussed in the broader context of those parts of North Head which are within Sydney Harbour National Park. Such an approach is appropriate for this Conservation Management Plan because the areas to the north and south of the Quarantine Station are