16 ANCIENT PLANTS 



Another kind of preservation is that which coats 

 over the whole plant surface with mineral matter, which 

 hardens, and thus preserves the form of the plant. 

 This process can be observed going on to-day in the 

 neighbourhood of hot volcanic streams where the water 

 is heavily charged with minerals. In most cases such 



Fig. 9. Clay Nodule split open, showing the two halves of the cone which was its. 

 centre. (Photo.) 



fossils have proved of little importance to science, 

 though there are some interesting specimens in the 

 French museums which have not yet been fully exa- 

 mined. A noteworthy fossil of this type is the Chara, 

 which, growing in masses together, has sometimes been 

 preserved in this way in large quantities, indicating the 

 existence of an ancient pond in the locality. 



There is quite a variety of other types of preser- 



