Howth Head, in the Nose of Howth group. Sandstone is also present, and the sea stacks are primarily formed from quartzite and sandstone. Embedded in the bedrock are a small range of minerals. Full fossils are scarce but there is a reasonable presence of trace fossils. Above the bedrock are deposits of glacial drift, from which the island's soils are also formed. The soils are siliceous and acidic. At Carrigeen Bay are sand and shingle, developing into low sand hills inland, with modest presence of marram-bound dune. There are no streams on the Eye but the island has one known regular spring, located 145 metres southeast of the site chosen for the Martello Tower. This spring was once substantial enough to fill a small pond, but the area around it has become sedimented and overgrown. The climate is similar to that of coastal Fingal, with a mean air temperature of 12 degrees Celsius. Summer has notable occurrence of westerly winds, while easterly winds are more common from February to May, but the overall leading winds are from the southwest. Habitats, fauna and flora Habitats In a survey in 2016, 11 land habitats and 4 maritime were identified; the marine aspect includes both intertidal and subtidal reefs, on the eastern edge of the island and in nearby waters. The terrestrial habitats include two types of grassland, three types of marsh, two rock types, two beach types, the stonework of the two buildings, and the dominant habitat, dense bracken cover with a bramble understorey. Flora The flora of the island differs considerably from that of Howth, partly due to island conditions, and to the large bird population and resulting guano. The primary vegetation types are bracken and dry grassland, notably of red fescue grass. Among the bracken plants are nettle, false oat-grass and hogweed, as well as some woodland species, lesser celandine and lords-and-ladies, and with rosebay willow herb (also known as fireweed) found at the edges of bracken patches. Bluebells and dog-violet are joined on thinner soils by the rare spring squill, and also mouse-ear and knotted clover. In some areas spear thistle and creeping thistle, and cow parsley, are also found. Elder and sycamore trees are found in small volume, and some rusty willow, ash, prunus and pyrus examples also. Additional plant types are found near and on the cliffs, including rock samphire, rock spurrey, tree mallow and sea lavender,