16 GEOLOGY OF THE ISLE OF WIGHT 



to see what the things we find have to tell us. The sort 

 of place where we should be most likely to find wood 

 floating in the sea to-day would be near the mouth of a 

 great river like the Mississippi or the Amazon, rivers 

 which bring down numerous logs of wood from the forest 

 country through which they flow. 



Examine the shales and limestone bands. On the 

 surface of some of the paper-shales are numbers of small 

 round or oval white spots. They are the remains of shells 

 of a very minute crustacean, Cypris and Cypridea, from 

 which the shales are known as Cyprid shales. In other 

 bands of shale are quantities of a bivalve shell called 

 Cyrena. There is a band of limestone made up of Cyrena 

 shells, containing also little roundish spiral shells called 

 Paludina.* This limestone resembles that called Sussex 

 or Petworth Marble, which is mainly composed of shells 

 of Paludina, but some layers also contain bivalve shells. 

 It is hard enough to take a good polish, and may be seen, 

 like the similar Purbeck marble, in some of our grand old 

 churches. Another band of limestone running through 

 the shales is made up of small oysters (Ostrea distorta). 



We shall see fossil shells best on the weathered surfaces 

 of rocks, i.e., surfaces which have been exposed to the 

 weather. One beginning geological study will probably 

 think we shall find fossils best by looking at fresh broken 

 surfaces of rock. This is not so. If you want to find 

 fossils, look at the rock where it has been exposed to the 

 weather. The action of the weather rain, carbonic 

 dioxide in the rain water, etc. is to sculpture the surface 

 of the rock, so that the fossils stand out in relief. A 

 weathered surface is often seen covered with fossils, when 

 a new broken one shows none at all. 



Many of the shells in the limestones are very like shells 

 which are found at the present day. We must know 



* The name now adopted is Viviparus. There is also a band of 

 ferruginous limestone mainly composed of Viviparus. 



