472 FOSSIL INVEKTEBRATED ANIMALS. 



jnasses — the vegetable tissue becomes altered in the trunks and 

 branches ; the substance of the hgneous layers, being much 

 more solid than that which fills their intervals, is decomposed 

 much more slowly than the latter. From this proceed those 

 concentric circles which give to those extraordinary incrusta- 

 tions the appearance of genuine petrifactions. But, however, 

 on examining them carefully, it is easy to see that those pre- 

 tended petrified trees are nothing but masses of a sandstone, 

 more or less hard^ which preserved only the form of the vege- 

 tables which have served them for moulds. 



Such are the observations of MM. Peron and Lesueur. In 

 adopting the views of those naturalists, then, we cannot con- 

 sider these trees as true petrifactions. We find in them, 

 however, a mode of incrustation altogether singular, and to 

 which we know of nothing analogous except what is remarked 

 on the roots of trees, which penetrate into a sandy and ferru- 

 ginous soil. An example of this is seen in the roots of oaks, 

 in the environs of the Sablonniere, of the marsh or pool of 

 Auteuil, in the Bois de Boulogne, near Paris. These roots 

 are changed into hollow tubes, which are tolerably thick, and 

 it is observed that the oxide of iron serves as a cement to unite 

 the quartzose particles. 



The second fact in favour of recent petrifactions is to be 

 found in the Biblioth^que Universelle for July, 1818. Mr. 

 Mackenzie describes there a petrified tree, which was observed 

 near Pennycuilk, ten miles from Edinburgh. The trunk 

 alone exists, which springs vertically from the ground some 

 feet. It is almost four feet in diameter from its base ; its roots 

 sink into the earth in different directions ; and, in a word, it 

 appears to have grown in the place in which it was found. Its 

 substance is now a genuine sandstone, and what remains of 

 the bark is in the state of pit-coal, as is often the case with 

 fossilized wood. 



In this fact there is an analogy with the one first cited, in 

 the circumstance of the substance of the tree itself being 



1 



