94 SIR G. S. MACKENZIE on the Formation of Chakedony. 



With respect to the size of the pendulous masses, I possess 

 one in which it does not exceed the fiftieth part of an inch in dia- 

 meter ; and another in which the diameter is one inch and three- 

 tenths; and I have seen some larger. In contemplating this 

 great difference in size, we naturally recur to the state in which 

 the substance was before it assumed its present form. We know 

 that, from a small quantity of a very weak solution of a salt, very 

 minute crystals will be formed ; while, from an equal quantity 

 of fluid more highly charged, larger crystals will shoot. But 

 there is a h'mit to this j for after passing a certain extent in add- 

 ing soluble matter, the resulting mass becomes confused. To pre- 

 vent this, when we wish to procure large crystals, we use a large 

 quantity of a rather weak solution, and allow it to evaporate 

 slowly. But supposing, as some have done, that pendulous Chal- 

 cedony is a crystalline shoot, we cannot, I suspect, accommodate 

 ourselves by supposing solutions of different strengths ; and if 

 we could, we see no means of carrying on a steady evaporation. 

 But as we know of no such thing as a cylindrical crystal, we may 

 at once set aside the idea of such a thing as chimerical. But it 

 is not, perhaps, easier to account for this form of Chalcedony, 

 with respect to difference of form in the pendulous specimens, by 

 means of a state of fluidity from heat. From an inspection of 

 the two specimens I have presented, a person, desirous of ac- 

 counting for the difference of size, by an appeal to heat, as the 

 sole cause of fluidity, would assert that the mass had been more 

 fluid in one case than in the other ; and that the minute forms 

 owed their origin to a great degree of fluidity, while the Chalce- 

 dony forming the larger specimen had not been subjected to a 

 greater degree of heat than was necessary to render it viscid. 

 This would be very plausible, were these the only specimens we 

 had to appeal to. But when we look farther, we find, in a small 

 specimen, such as that which I now submit to the inspection of 

 the Society, the pendulous masses varying very much in size, 



