SIR G. S. MACKENZIE on the Formation of Chalcedony. 83 



be permitted to hesitate to fix our belief, until we are admitted 

 farther into the secrets of Nature. 



It will be allowed, that all attempts to account for what we 

 see in the material world, however unsuccessful they may be, are 

 so many steps 'towards discovery. The failure of one leads to 

 another. The naturalist is situate as if he were standing on a 

 spot whence numerous roads diverge, but of which only one leads 

 directly to Truth. He travels over many of them without ha- 

 ving struck into the right one ; but he gains at least the satis- 

 faction of having reduced the number yet to be examined, and 

 to have increased the chance of success to future adventurers. 



The means by which Silica may be reduced into a condition, 

 from which it may assume the forms of chalcedony, of flint, of 

 crystals, or in which it may be introduced into the minute pores 

 of animal and vegetable bodies, may long continue to be a mys- 

 tery. We may hope, however, that the discovery of these means 

 may yet exalt the name of some fortunate philosopher, who, with 

 talent, observation, judgment, and perseverance, such as have 

 displayed to an admiring world the nature of the alkalies and 

 earths, will reduce the opacity of the veil that conceals some of 

 the most important and most wonderful operations of Nature. 



Geological theorists have, in their anxiety to generalise, been 

 too prone to attribute all appearances to one proximate cause. 

 WERNER looked only to one cause, the solvent power of water ; 

 but water refuses to perform what has been ascribed to its power. 

 HUTTON regarded fluidity, caused by heat, and modified by com- 

 pression, as sufficient to account for every thing, while it is 

 speedily obvious to a careful observer, that the number of the 

 phenomena which can be best explained by the agency of heat, 

 is limited. The absurdities which have been published, for the 

 purpose of accommodating the theory of aqueous solution to 

 facts which bear the impress of a different process, are now ra- 



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