OF ORGANIC NATURE. 45 



Almost all the hard parts of animals — the bones and 

 so on — are composed chiefly of phosphate 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 structures that have become imbed- 

 ded in the way I have described, 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 back- 

 bone 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 dis- 

 solved all the phosphate and carbonate of lime, and the 

 bones themselves had thus decayed and entirely dis- 

 appeared ; but as the sandstone happened to have con- 

 solidated 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 whatsoever 

 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 have entirely 

 perished, and left no trace whatever of their forms, may 

 be proved to you by other considerations. There are 



