328 



dermis of the cane yielded 9 grains of silex. He also found it in 

 English reeds and grasses, and in oats, wheat, barley, &c. in a suffi- 

 cient quantity to yield glass with the blow-pipe ; a* straw being thus 

 converted into a fine globule of glass : the epidermis of the equisetum 

 hyemale, or Dutch rush, appearing to consist almost entirely of 

 silex *. 



Presuming, therefore, that the silicious induration of various 

 substances will be allowed to have proceeded from a deposition of 

 silex, from its solution in water, I shall, in my next, proceed to 

 apply this principle, whilst endeavouring to account for the forma- 

 tion of silicized wood. 



Yours, &c. 



LETTER XXXIII. 



PETRIFIED WOOD. ...DIVIDED INTO SILICIOUS, CALCAREOUS, ALU- 

 MINOUS, &C SILICIOUS DIVIDED INTO SILICIZED WOOD AND 



SILICIZED BITUMINOUS WOOD. ...THE LATTER, INTO CALCEDO- 

 NIC, AGATINE, JASPERINE, AND OPALINE. 



-T OR those substances which bear the nfarks of having originally 

 existed as wood, but which now possess a' stony hardness, from the 

 introduction of different earthy matters, it seems proper to retain 



* Nicholson's Journal, May, 1799. 



