vii THK NATURE A OF FOS* Si 



.'..- sculpturing, while the surrounding limestone has 

 been slowly dissolved and removed (Fig. 15). In other 

 cues the material of the organisms has been less 

 durable than that of the surrounding matrix, and mere 

 moulds of the fossils are preserved By pressing wax 



Fi. iyFaib ttaadiag ia ralMf on weathered or(ac of UMMMOM. 



i ted gutta perc ha into these moulds, casts may be 

 icd. In this way a rock which may have been sup- 

 posed to be unfossiliferous by one observer is shown by 

 another of greater training to be full of fossils. Old 

 walls and buildings, the refuse heaps of old quarries, the 

 angular blocks strewn at the base of a cliff in short, 

 all surfaces of rock which have been lying exposed for a 

 long while to the gentle influences of the air, rain, and 

 frosts, may be made to yield their evidence as to the 

 fossils in the rocks of a 



c 



