360 



tions in such a manner as to ascertain what volatile matters enter 

 into their composition, would, perhaps, sometimes evince the un- 

 expected presence of bitumen both in horn-stone and flint. 



Yours, &e. 



LETTER XXX VIII. 



CALCAREOUS WOOD. ... DIM E FREQUENTLY HELD IX SOLUTION, IN 



WATER VARIOUS FORMS OF DE POSIT ION.... CONFETTO DI T1VOL1 



....QUARRIES OF TUFACEOUS STONE... .STALACTITIC CAVERNS. 







1 HE mineralized wood, of which we shall treat in this Letter, is 

 of such a nature as will not oppress us with such difficulties, whilst 

 endeavouring to ascertain its mode of formation, or the nature of 

 its constituent parts, as were opposed to our inquiries, respecting 

 the same subjects, whilst examining silicious wood ; ^ince the na- 

 ture of the mineralizing matter is such as to allow of its removal by 

 such agents as will not act-so destructively on the vegetable matter, 

 which forms the substratum of the fossil. 



CALCAREOUS WOOD, wood impregnated with lime, is neither so 

 hard nor so heavy, as silicious wood ; it may be scratched by a 

 knife even in its hardest parts ; and in some parts will allow of 

 being cut, almost like recent wood; its hardness and its gravity, 



