24 GEOLOGY OF THE ISLE OF WIGHT 



A pretty little coral, looking like a collection of little stars, 

 Holocystis elegans, one of the Astraeidae, is often very 

 sharply weathered out. 



Above the Perna bed lies a mass of blue clay, weather- 

 ing brown, called the Atherfield clay, because it appears 

 on a great scale at Atherfield on the south west of the 

 Island. It is very like the clay of the Wealden shales, 

 but is not divided into thin layers like shale. 



Next we come to the fine mass of red sandstone which 

 forms the vertical wall of Red Cliff. Not many fossils 

 are to be found in these strata. Let us note the beauty 

 of colouring of the Red Cliff pink and green, rich orange 

 and purple reds. And then let us pass to the other side 

 of the anticline, and walk on the shore to Shanklin. Here 

 we see the red sandstone rocks again, but now dipping 

 to the south. You probably wonder why these red cliffs 

 are called Greensand. But look at the rocks where they 

 run out as ledges on the shore towards Shanklin. Here 

 they are dark green. And this is really their natural 

 colour. They are made of a mixture of sand and clay 

 coloured dark green by a mineral called glauconite. 

 Grains of glauconite can easily be seen in a handful of 

 sand, better with a magnifying glass. This mineral is 

 a compound of iron, with silica and potash, and at the 

 surface of the rock it is altered chemically, and oxide of 

 iron is formed the same thing as rust. And that colours 

 all the face of the cliff red. The iron is also largely re- 

 sponsible for our finding so few fossils in these strata. 

 By chemical changes, in which the iron takes part, the 

 material of the shells is destroyed.* Near Little Stairs 

 hollows in the rock may be seen, where large oyster shells 

 have been. In some you may find a broken piece of shell, 

 but the shells have been mostly destroyed. Nearer 



* Carbonate of lime has been replaced by carbonate of iron, and 

 the latter converted into peroxide of iron. At Sandown oxidation 

 has gone through the whole cliff. 



