27 



bourhood of coal. These remains, as have been already 

 mentioned, are of various gramina, cryptogami and suc- 

 culent plants. On allowing some of these bodies to re- 

 main in water, their substance becomes softened down, and 

 is resolved into a mass in which the vegetable matter is 

 obvious. 



2. Aluminous wood. The wood which has been thus 

 named by different authors, by its proneness to combustion, 

 and by the other properties which they describe it to 

 possess, should be considered as pyritous wood, having ob- 

 tained its change in the ferruginous clay in which it has 

 been imbedded. 



The mineralizing matter of metallic fossil vegetables is 

 most commonly the pyrites or sulphurets and carbonates of 

 iron, copper, zinc, or lead. 



I. FERRUGINOUS FOSSIL WOOD. 



1. Pyritical. In this fossil the sulphuret of iron per- 

 vades the charcoal into which the vegetable matter has 

 been converted. When first found, it generally possesses 

 metallic brilliancy, is sufficiently hard to scratch glass, 

 emits sparks on collision with steel, and displays the 

 forms and markings pointing out its vegetable origin ; but 

 it soon begins to suffer from decomposition, when its cha- 

 racters change, and it finally resolves into a saline flocculent 

 substance. 



2. Carbonated. In these specimens, which are of dif- 

 ferent shades of brown colour, and generally of an uniform 

 substance, the marks of the vegetable origin are easily 

 observable, although not so distinct as in the specimens of 

 the preceding species before the commencement of de- 

 composition. 



II. FERRUGINOUS FOSSIL SEEDS, &c. 



Innumerable seeds, seed-vessels, &c. have been found, 

 by Mr. Crow and others, in the blue clay of Sheppey, in 

 the state of pyrites. Most of these belong to plants 



