334 



produced by the filling up of little cracks in the stone, by a sub- 

 sequent infiltration of a. silicious fluid. Its fracture is conchoidal, 

 very rarely splintery ; its lustre is dull, and its hardness varies with 

 its proportion of silex. The general characters and properties are 

 such, as readily lead to a knowledge of the nature of its composi- 

 tion. The veined or cloudy appearance of these stones rnay, in gene- 

 ral be very easily traced to the introduction of fine earthy particles, 

 between the detached masses of bituminized fibres of the fossil 

 wood, which have been all consolidated together by a subsequent 

 infiltration of a solution of silex. The specimen, of which the po- 

 lished section is figured at Plate II. Fig. 8. will serve to point out 

 how much this opinion is favoured by the appearances yielded by 

 this species of wood. The examination of jaspers has shown that 

 they generally contain silex and alumine, and even other earths, in 

 different proportions ; whilst the, folio wing experiments corroborate 

 the idea of bituminous matter entering, in a small proportion, into 

 the composition of this species of fossil wood. 



Sixty grains of jasperized wood, reduced to powder, were mixed 

 with double the quantity of purified pot-ash, purified by Mr. Allen, 

 to which was added a sufficient quantity of distilled water, to dis- 

 solve the pot-ash. The powder which settled, and which was nearly 

 white when dry, but became darker on being wetted, in about four 

 or five days, showed a line of darker matter on the surface of the 

 precipitate ; which, during a month, continued to increase, when it 

 seemed to constitute, in bulk, about one fourth of the whole preci- 

 pitate. Half this precipitate, added to colourless sulphuric acid, 

 evidently darkened it : but willing to avail myself of the kindness of 

 my friend Mr. W. H. Pepys, whose well-known abilities would stamp 

 unquestionable authority on the results of his experiments, I re- 

 quested that gentleman to subject the remainder to an examination, 

 for the purpose of ascertaining the presence of carbon. According 

 to his obliging communication the separated precipitate, after 



