SIR G. S. MACKENZIE on the Formation of Chalcedony. 99 



I will now exhibit a few specimens of the parallel form, 

 which present facts altogether anomalous with respect to the 

 laws which fluids in general obey. In the first, we see that the 

 surface of the Chalcedony forming the undermost layer is not 

 parallel with that of the uppermost, and the intermediate layer , 

 of opal consequently takes the form of a wedge. In the next, 

 this kind of anomaly is still more remarkable, and cannot be ex- 

 plained by any effects which come under our ordinary observa- 

 tion *. 



We observe in this specimen, that the upper part of the pa- 

 rallel form has been depressed in a singular manner by the mat- 

 ter forming a pendulous mass. It seems as if the depressed mat- 

 ter had disappeared ; for, on the other side of the cavity, the 

 coats follow the usual course. I confess that I am quite puzzled 

 by this specimen. One thing, however, seems evident, that the 

 matter had not been in a state of great fluidity. 



I am now to shew a specimen which appears to indicate a 

 state of viscid fluidity ; or that state in which we observe glass 

 when under the hands of the blower. In this we have the pen- 

 dulous form thickened at the end, so as to resemble a drum- 

 stick. As the pendulous mass has come into contact with the 

 matter below, we may either suppose that this has caused the 

 thickening at the end, or that this shape had been assumed, as 

 glass assumes it when dropt, and also thick honey. I cannot 

 imagine this specimen to have been in any other state ; and I 

 have longed to possess another similar one, that I might exa- 

 mine the internal structure ; for I cannot reconcile myself to the 

 risk of losing that now before the Society, by attempting to cut 



* Though in most cases it is exceedingly difficult to make intelligible drawings 

 of the minute appearances which Chalcedony presents, a delineation of the fact now 

 under consideration is easy, and it is given in Plate V. Fig. 1. 



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