10 ANIMALS OF THE PAST 



pletely and minutely may this change occur 

 that under the microscope the very cellular 

 structure of the wood is visible, and as this 

 varies according to the species, it is possible, 

 by microscopical examination, to determine 

 the relationship of trees in cases where noth- 

 ing but fragments of the trunk remain. 



The process of fossilization is at best a slow 

 one, and soft substances such as flesh, or even 

 horn, decay too rapidly for it to take place, so 

 that all accounts of petrified bodies, human or 

 otherwise, are either based on deliberate frauds 

 or are the result of a very erroneous misinter- 

 pretation of facts. That the impression or 

 cast of a body migJit be formed in nature, 

 somewhat as casts have been made of those 

 who perished at Pompeii, is true ; but, so far, no 

 authentic case of the kind has come to light, 

 and the reader is quite justified in disbelieving 

 any report of " a petrified man." 



Natural casts of such hard bodies as shells 

 are common, formed by the dissolving away of 

 the original shell after it had become enclosed 

 in mud, or even after this had changed to 

 stone, and the fiUing up of this space by the 



