258 THE WORLD'S LUMBER ROOM. 



trunk is neither mineralised by infiltration, nor merely repre- 

 sented by a cast, but the whole of its organisation is faith- 

 fully reproduced. A cast may give one a perfect idea of the 

 appearance of any object, as seen from within or from without, 

 but cannot show its structure ; whereas a model, which is 

 what this sort of petrifaction produces, is an exact imitation. 

 Each atom of the original substance is replaced by an atom 

 of some other mineral. The most common replacement is 

 that in which silica is substituted for lime, the former being, 

 as we have seen, especially attracted by decaying matter. 

 Strictly speaking, these fossils are not therefore organic re- 

 mains, but perfect models of such remains. 



Some few extinct animals are represented, however, by 

 more than fossils, and more even than bones. Early in the 

 present century, the first mammoth, still covered with flesh, 

 hair, and wool, was discovered in the ice by a Siberian 

 fisherman, who possessed himself of its two great ivory 

 tusks, which he sold for fifty roubles, and left the carcass 

 for the white bears and dogs to feast upon. Two years 

 later, in 1805, the skeleton was still almost entire. The 

 animal measured sixteen feet in length and nine in height, 

 and from the long, stiff, black bristles and coarse red-brown 

 hair and wool still remaining, it was evident that it was a 

 species of elephant fitted to live in cold regions. 



Long before it attracted the notice of naturalists, the 

 mammoth had been known to the Siberian Ostyaks, who 

 were so accustomed to finding the carcases buried and 

 preserved in the frozen ground, that they firmly believed 

 that the creatures lived there, and only died when they smelt 

 the air. Its long curved tusks they considered to be movable 



