104 SIR G. S. MACKENZIE on the Formation of Chalcedony. 



party sounds in matters of science, in which its origin can only 

 be found in ignorance. Our knowledge of the structure of the 

 crust of the globe is now so extensive, that, in endeavouring to 

 account for the mode of its formation, we should feel ashamed to 

 limit our views to any single agent or process. With respect to 

 minute modes of formation in regard to individual minerals, the 

 description I have given in this memoir will, I trust, prove the 

 inutility of considering them, until experiments shall have enti- 

 tled us to speak freely. If it does so, one object I have had in 

 view will have been accomplished. 



