C 4°7 3 
XXIII. Observations on the fossil Bones presented to the Royal 
Society by his most Serene Highness the Margrave of Anspach, 
&c. By the late John Hunter, Esq. F. R. S. Communicated 
by Everard Home, Esq. F. R. S. 
Read May 8, 1794. 
The bones which are the subject of the present paper, are to 
be considered more in the light of incrustations than extra- 
neous fossils, since their external surface has only acquired a 
covering of crystallized earth, and little or no change has taken 
place in their internal structure. 
The earths with which bones are most commonly incrusted 
are the calcareous, argillaceous, and siliceous, but principally 
the calcareous ; and this happens in two ways ; one, the bones 
being immersed in water in which this earth is suspended ; 
the other, water passing through masses of this earth, which it 
dissolves, and afterwards deposits upon bones which lie under- 
neath. 
Bones which are incrusted seem never to undergo this 
change in the earth, or under the water, where the soft parts 
were destroyed ; while bones that are fossilized become so in 
the medium in which they were deposited* at the animal’s 
death. The incrusted bones have been previously exposed to 
* Bones that have been buried with the flesh on, acquire a stain which they never 
lose; and those which have been long immersed in water, receive a considerable tinge. 
