SIR G. S. MACKENZIE on the Formation of Chalcedony. 97 



The result of this accident shews a much more intimate connec- 

 tion than our eyes could before discover. It exhibits a process, 

 the steps of which are so distinct, as to lead immediately to a 

 mode of formation similar to the stalactitic. It appears that the 

 first formed portion of the pendulous mass had reached lower 

 than the subsequent coatings ; and that the matter, in its liquid 

 form, after depositing a coat on the pendulous mass, had spread 

 out horizontally to form parallel layers. The extreme thinness of 

 some of the coats indicates an extreme degree of fluidity ; while 

 the accuracy with which the right angle is preserved between 

 the descending coat and the horizontal layers is very striking ; 

 and hence we may conclude (as well as from the uniform thick- 

 ness of each layer), that the passage from fluidity to a state of 

 solidity must have been rapid. This conclusion leads us to ano- 

 ther, I think irresistibly, that Chalcedony has been fluid per se, 

 and that it has become solid in the same manner as tallow, wax, 

 or water when it passes into the state of ice. But before pro- 

 ducing specimens to confirm that conclusion, I must point out 

 another fact which the specimen now before us has brought to 

 light. It appears distinctly, that the fluid matter has not only 

 enlarged the pendulous mass, and thickened the mass at the bot- 

 tom by successive descending coats, but that each coat or layer 

 may be traced round the sides of the cavity ; and, as might have 

 been expected, there is a greater accumulation at the bottom 

 than on the pendulous mass and sides of the cavity. Thus, no 

 doubt is left of the mode of formation. 



In the next specimen which I exhibit, we have some other 

 curious facts displayed, besides a remarkable example of what I 

 have been illustrating. In this we see the successive descent of 

 the coats along the sides of the cavity. But it appears that a 

 considerable quantity of Chalcedony had been previously intro- 

 duced in some other manner, and which has assumed the parallel 

 form at the bottom. The regular formation of the parallel form, 



VOL. x. P. i. N 



