350 THE CAUSES OF THE xi 



of lime and carbonate of lime. Some years ago, 

 I had to make an inquiry into the nature of some 

 very curious fossils sent to me from the North of 

 Scotland. Fossils are usually hard bony structm*es 

 that have become imbedded in the way I have de- 

 scribed, and have gradually acquired the nature and 

 solidity of the body with which they are associated ; 

 but in this case I had a series of holes in some 

 pieces of rock, and nothing else. Those holes, 

 however, had a certain definite shape about them, 

 and when I got a skilful workman to make castings 

 of the interior of these holes, I found that they 

 were the impressions of the joints of a backbone 

 and of the armour of a great reptile, twelve or more 

 feet long. This great beast had died and got 

 buried in the sand ; the sand had gradually 

 hardened over the bones, but remained porous. 

 Water had trickled through it, and that water 

 being probably charged with a superfluity of 

 carbonic acid, had dissolved all the phosphate and 

 carbonate of lime, and the bones themselves had 

 thus decayed and entirely disappeared ; but as 

 the sandstone happened to have consolidated by 

 that time, the precise shape of the bones was 

 retained. If that sandstone had remained soft a 

 little longer, we should have known nothing what- 

 soever of the existence of the reptile whose bones 

 it had encased. 



How certain it is that a vast number of animals 

 which have existed at one period on this earth 



