Among other objects of interest along this Wealden shore may be noticed a curious transformation which has affected the surface of some of the shell limestones after they were formed, which is known as cone-in-cone structure. It has quite altered the outer layer of the rock, so that all trace of the shells of which it consists is obliterated. Numerous pieces of iron ore from various strata lie on the shore. Through most of English history the Weald of Kent and Sussex was the great iron-working district of England. The ore from the Wealden strata was smelted by the help of charcoal made from the woods that grew there, and gave the district its name;--for _Weald_ means "forest." This industry gradually ceased, as the much larger supplies of iron ore found near the coal in the mines of the North of England came to be worked. Iron pyrites, sulphide of iron in crystalline form, was formerly collected on the Sandown shore, and sent to London for the manufacture of sulphuric acid. This mineral is often found encrusting fossil wood. It also occurs as rounded nodules (mostly derived from the Lower Chalk) with a brown outer coat, and often showing a beautiful radiated metallic structure, when broken. (This form is called marcasite.) As we walk by the edge of the water, we shall see what pretty stones lie along the beach. When wet with the ripples many look like polished jewels. Some are agates, bright purple and orange in colour, some clear translucent chaldedony. We shall have more to say about these later on. They do not come from the Wealden, but from beds of flint gravel, and are washed along the shore. But there are also jaspers from the Wealden. These are opaque, generally red and yellow. There are also pieces of variegated quartz, and other beautiful pebbles of various mineral composition. These are stones from older rocks, which have been washed down the Wealden rivers, and buried in the Wealden strata, to be washed out again after hundreds of thousands of years, and rolled about on the shore on which we walk to-day. [Footnote 1: Blue clays of various geological age, which in wet weather become semi-liquid, and flow out on to the shore, are known in the Island by the local name of _Blue Slipper_.] [Footnote 2: The name now adopted is _Viviparus_. There is also a band of ferruginous limestone mainly composed of _Viviparus_.] [Illustration: PL. II] Trigonia Caudata Trigonia Daedalea Gervillia Sublanceolata (Ammonite) Nautilus Radiatus Mortoniceras Rostratum LOWER AND UPPER GREENSAND Chapter IV THE LOWER GREENSAND