OF ORGANIC NATURE. 45 



of which we cannot reasonably expect to find any 

 traces whatever : there is nothing of them to preserve. 

 Within a very short time, you will have noticed, after 

 they are removed from the water, they dry up to a 

 mere nothing ; certainly they are not of a nature to 

 leave any very visible traces of their existence on such 

 bodies as chalk or mud. Then again, look at land ani- 

 mals ; it is, as I have said, a very uncommon thing to 

 find a land animal entire after death. Insects and 

 other carnivorous animals very speedily pull them to 

 pieces, putrefaction takes place, and so, out of the hun- 

 dreds of thousands that are known to die every year, 

 it is the rarest thing in the world to see one imbedded 

 in such a way that its remains would be preserved for 

 a lengthened period. Not only is this the case, but 

 even when animal remains have been safely imbedded, 

 certain natural agents may wholly destroy and remove 

 them. 



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 



