FROF. W. ('. WILLIAMSON UN MINERALIZATION. 196 



some cases, as amongst shells and the bones of animals, these 

 changes were limited to the disappearance of the decomposable 

 organic matter, leaving the mineral elements unaltered. Still 

 further changes depended upon the varieties of local circum- 

 stances and conditions existing in each individual case. The 

 imbedded object might undergo no change. It might for a time 

 only have any cavities that existed in its substance, large or 

 small, filled up by inorganic matter introduced into those 

 cavities in a state of solution, and left there either in an amor- 

 phous or a crystalline condition. 



In other cases, the substances composing the buried organism 

 might be partially or wholly removed, either in a solvent or a 

 gaseous condition, and the vacant spaces be reoccupied by 

 foreign materials as before. All these varying results must 

 have been dependent, partly upon differences in the character 

 of the matrix within which the organism was imbedded, partly 

 in the substances dissolved in the superincumbent water, and 

 partly upon differences existing between the affinities of the 

 substances so dissolved and those of the buried object which 

 they were about to replace. 



