CHALK AND LIMESTONE. 



569 



or sand grains or that curious bit cf conglomerate ? Perhaps the reader 

 may be at Ramsgate or Margate or another place where the " white cliffs 

 of Albion " glisten in the sun. Take up a piece of chalk and examine 



Fig. 641. Cliffs showing strata. 



it It is soft and soils your hands, and you will throw it away, perhaps but 

 don't. Take it home and put it under the microscope or a good magnifying 

 glass. What do you see ? 



You will find the remains of animals that is, shells and tiny bits of 

 coral packed close together. Under the 

 microscope they will become more sepa- 

 rated, and the grains will be distinct 

 fragments of shells, etc. If this little 

 bit of chalk be composed of marine 

 animals' shells, of course the whole cliff 

 is composed of the same kind of material. 

 But how did the shells get into the chalk ? 

 Shells are chalk carbonate of lime ; 

 lime was deposited at the bottom of the 

 sea, and the infinite millions of minute 

 animals formed themselves shells, and 

 left them to be piled up by Nature's forces into cliffs during countless 

 ages. 



Yes, but how did the lime get into the water to make the shells ? We 

 will endeavour to explain. Rain, when falling, takes some carbonic acid 

 from the air, which we know contains it. This acts upon the lime in the 

 rocks (lime is oxide of calcium, and calcium is an element in the earth), so we 

 get a bi-carbonate of lime (soluble in water), which rises from the rocks in 

 springs. These springs and their streams deposit lime, as we can see in 

 caverns where we find stalactites and stalagmites. The lime is transmitted 



Fig. 642. Limestone with encrinites. 



