142 TRANSACTIONS OF THE [1891 



it were, with green only. We liave here, therefore, a phe- 

 nomenon, of another kind due to "anomalous dispersion." 



In all jDrevious apophyllites, it would therefore seem that 

 the dispersion conforms to the positive end of the Spec- 

 trum and the rings are hlacli lined with greenish yellow; 

 whereas in the present case we have another sort of effect, 

 a black cross and Rainbow Bings. For my part says 

 Hastings, it seems extremely difficult to imagine how the 

 habit of a crystal could be so completely changed. 



Dr. Steeg suggests that we might find in the chemical 

 composition of the Apophyllite from the New Almaden 

 Mine, an explanation of its optical properties. Thus the 

 analysis of the Older Apophyllite as given by Dana 16 : 

 Edition 1891, is 



Silica - - - - 52.97 



Lime, _ _ . _ 24.72 



Potass, - - - . 5.20 



Water, - _ _ . 19.50 



Fluorine, - - - 2.10 



100.89 



A silicate; but to establish comparison, Dr. David T. 

 Day undertook to have an analysis made in the U. S. 

 G-eological Department. This he will do immediately. 



To sum up, therefore, we have in the Apophyllite of 

 the New Almaden Quicksilver Mine, a new sort of Apo- 

 phyllite, or at all events, one now mentioned for the first 

 time. 



Baltimoke, October 1st, 1891. 



