Page:VCH Sussex 1.djvu/53

 GEOLOGY certain thin beds are so full of the coin-shaped nummulites or of the spindle-shaped Aheolina as to have become sandy limestones, while another bed is composed principally of the large handsome shells of Cardita planicosta. The fauna is extremely varied and has been care- fully studied by the Rev. O. Fisher ' and Dixon." Mr. Fisher has made out a definite succession in the zones, certain fossils being characteristic of particular horizons throughout the Hampshire basin ; but it is not yet clearly understood to what extent these variations are the result of local conditions or of the lapse of time. Species confined to one thin bed in Selsey elsewhere have often much wider ranges. The constant changes in the character of the sediments, and probably in the saltness of the water, are enough to account for the appearance and disappearance of many of the more sensitive species. Taking the strata in order, commencing with the lowest seen on the shore near Chichester Channel, we first meet with sandy loams with flint pebbles and much worm-eaten driftwood. This pebble bed is apparently the same as that forming the base of the Bracklesham Series in the Isle of Wight. Then follow bedded carbonaceous clays and sands, with much driftwood and an occasional oyster, till near West Witter- ing Beacon we find a sand full of the drifted fruits of the nipa-palm. This is a nut about the size of and somewhat like the cocoanut. A living species closely allied to the extinct form found at West Wittering is a low palm which always grows in tidal estuaries of the East Indies, dropping its nuts into the water in such profusion as to become an obstruction to the paddle-steamers which navigate these estuaries. The extinct species of Nipa, of which several have been found in Britain, seem all to have grown in similar positions, for they are found associated with oysters and TeredoAioxt^ driftwood, not with plants and animals belonging entirely to the land or to fresh water. More to the south, and consequently higher in the series (the dip is southward), follows bed after bed of carbonaceous clay and glauconitic sand, with driftwood and a few marine shells, till opposite Bracklesham farm commence the shelly beds from which most of the fossils are obtained. These continue to Selsey Bill, where the highest Eocene deposit in Sussex is met with in the Alveolina limestone of the Mixen Rocks, where it was formerly much quarried for building purposes. The slightest acquaintance with the natural history of warmer regions brings out in a most striking manner the resemblance of the Bracklesham animals and plants to those of the tropics, and their comparatively small connection with the existing fauna and flora of Britain. Amongst the vertebrate animals the turtles, crocodiles, sea-snakes, and large sharks and rays find their nearest living allies in the tropics. The mollusca are distinctly sub-tropical, including numerous nautili, volutes, cones, mitres, olives, cowries, and other large and handsomely sculptured shells. True 1 Quart. Joum. Geol. Soc. xviii. 65 (1862). ^ Geology of Sussex, ed. 2, 410, London (1878); see also Reid, 'Geology of Bognor,' pp. 4-8, Mem. Geol. Survey (1897). 15