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



by the descent of successive coats along the sides, and their 

 spreading over the bottom, appears in this specimen to have 

 been interrupted, by the introduction of another substance in a 

 fluid state, between which and the Chalcedony there seems to 

 have been a repugnance, analogous to that manifested between 

 oil and water. It has evidently not entered by the sides, nor 

 along with the Chalcedony (at least so far as we can judge while 

 we do not possess the whole geode), but it appears to have mixed 

 with the Chalcedony after it had been introduced, and to have 

 interrupted the regular formation of the parallel form, in a man- 

 ner which cannot be explained. 



Each successive layer of Chalcedony has insulated a portion 

 of the white substance, and at the bottom we see a layer of 

 quartz thus insulated. Though the regularity of the parallel 

 form is interrupted, the connection of the successive coats is not 

 prevented. 



Before quitting this specimen, I have to remark, that at one 

 side there appears some threads of foreign matter, around which 

 the Chalcedony had formed in the pendulous shape, before that 

 forming the interior mass had been introduced ; and from the po- 

 sition of these, it seems as if that of the cavity had been changed. 

 Another curious thing to be observed is, that the accumu- 

 lation of matter from one of the side coats, immediately below 

 the white matter (which is to all appearance zeolite), has in- 

 cluded in it a number of white hemispherical bodies, which seem 

 to indicate the incipient secretion, or rather separation of the 

 substance which usually forms some of the layers of the parallel 

 form. In another specimen, bodies similar to them appear to be 

 formed of a number of concentric hemispheres. Such facts, how- 

 ever, though curious, do not lead to the principal object I have 

 in view, which is, if possible, to demonstrate the kind of fluidity 

 to which the matter forming Chalcedony has been subjected. 



