THE LOWER GREENSAND 25 



Shanklin we shall find large oysters, Exogyra sinuaia, in the 

 rock ledges exposed at low tide. Some are stuck together in 

 masses. Evidently there was an oyster bank here. And 

 here the shells have not been destroyed like those in the cliff. 



From black bands in the cliff water full of iron oozes 

 out, staining the cliff red and yellow and orange, and 

 trickling down, stains the flint stones lying on the shore 

 a bright orange. At the foot of the cliff you may some- 

 times see what looks like a bed of conglomerate, i.e., a 

 bed of rounded pebbles cemented together. This does 

 not belong to the cliff, but is made up of the flint pebbles 

 on the shore, and the sand in which they lie, cemented 

 into a solid mass by the iron in the water which has 

 flowed from the cliff. It is a modern conglomerate, and 

 shows us how old conglomerates were formed, which we 

 often find in the various strata. The cement, however, 

 in these is not always iron oxide. It may be siliceous or 

 of other material. The iron-charged water is called 

 chalybeate ; springs at Shanklin and Niton at one time 

 had some fame for their strengthening powers. The 

 strata we have been examining are known as the Ferru- 

 ginous sands, i.e., iron sands (Lat. ferrum, " iron "). 

 Beyond Shanklin is a fine piece of cliff. Look up at it, 

 but beware of going too close under it. The upper part 

 consists of a fine yellow sand called the Sandrock. At 

 the base of this are two bands of dark clay. These bands 

 become filled with water, and flow out, causing the sand- 

 rock which rests on them to break away in large masses, 

 and fall on to the beach. 



It is clay bands such as these which are the cause of 

 our Undercliffs in the Isle of Wight. Turn the point, 

 and you see exactly how an undercliff is formed. You 

 see a wide platform at the level of the clay, which has 

 slipped out, and let down the sandrock which rested on it. 

 Beyond Luccombe Chine a large landslip took place in 

 1910, a great mass of cliff breaking away, and leaving a 



