FOSSILS, AND HOW THEY ARE FORMED 9 



limonite iron ore; and yet we know that these bones 

 have been buried within quite recent times. 



Sometimes we hear of springs or waters that "turn 

 things into stone/' but these tales are quite incorrect. 

 Waters there are, like the celebrated hot springs of 

 Auvergne, France, containing so much carbonate of 

 lime in solution that it is readily deposited on objects 

 placed therein, coating them more or less thickly accord- 

 ing to the length of time they are allowed to remain. 

 This, however, is merely an encrustation, not extending 

 into the objects. In a similar way the precipitation of 

 solid material from waters of this description forms the 

 porous rock known as tufa, and this often encloses moss, 

 twigs, and other substances that are in no way to be 

 classed with fossils. 



But some streams, flowing over limestone rocks, take 

 up considerable carbonate of lime, and this may be 

 deposited in water-soaked logs, replacing more or less 

 of the woody tissue and thus really partially changing 

 the wood into stone. 



The very rocks themselves may consist largely of 

 fossils; chalk, for example, is mainly made up of the 

 disintegrated shells of simple marine animals called 

 foraminifers, and the beautiful flint-like " skeletons" of 

 other small creatures termed radiolarians, minute as 

 they are, have contributed extensively to the formation 

 of some strata. 



Even after an object has become fossilized, it is far 

 from certain that it will remain in good condition until 

 found, while the chance of its being found at all is ex- 

 ceedingly small. When we remember that it is only here 

 and there that nature has made the contents of the rocks 

 accessible by turning the strata on edge, heaving them 

 into cliffs or furrowing them with valleys and canyons, 

 we realize what a vast number of pages of the fossil 



