383 



the thickness of a shilling, all over the woody part with the bark ; 

 the marks of the axe also remaining very conspicuous, with this 

 petrified crust upon it. By what means it should thus happen 

 cannot well be conceived, in regard there is no water near it, the 

 part above the ground, and out of the weather; the tree yet grow- 

 ing ; unless being cut at some season, when the sap was flowing, the 

 oozing of the sap might become petrified by the air, and the tree 

 grow rotten and hollow inward since that time ; which how long 

 since is not known. 



" A piece of that part cut was presented, together with this ac- 

 count, to the Royal Society, for their repository *." 



Aluminous fossil wood is mentioned by several authors : Mr. Walch 

 describes it as being of a brown colour, of a light weight, and pos- 

 sessing sufficient of its vegetable structure to demonstrate its origin ; 

 he also relates, that when considerable quantities of it are exposed 

 to the air, that it will take fire spontaneously. Besides being found 

 in various parts of England, it is found in considerable quantities 

 at Commadau and Altsattel, in Bohemia : near Hainfield, in Lower 

 Austria; at Weisner, in Hesse; and near Duben, in Saxony. 



The spontaneous inflammation of this species of wood, and the 

 use to which it is applied, the fabrication of alum, manifest that it 

 is a pyritous wood blended with clay. The chief component parts 

 of alum (the sulphate of alumine) are the acid of sulphur and the 

 earth, alumine; the former of which is derived from the sulphur 

 contained in the pyrites ; and the latter from the clay, of which it 

 constitutes by far the greatest part. 



What other earths enter into the composition of fossil woods, 

 and in what proportion, must be determined by future analyses. 



Philosophical Transactions, No. 19, Nov. 1666. 



