132 



W. Cross — Igneous Rocks in Wyoming. 



gopite, these elements may be calculated out, leaving only silica, 

 alumina and the alkalis in considerable amounts. Alumina is 

 found to be insufficient to combine with the alkalis in leucite 

 or sanidine, but if the S0 3 is present in noselite the alumina is 

 almost exactly sufficient. There is a large excess of silica, 

 enough indeed to have formed sanidine with all the alumina 

 and alkalis. 



Calculation of Analysis III. 



Molec. ratio. 



Diopside. 



Phlogopite. 



Noselite. 



Leucite. 



Apatite. 



Residue. 



Si0 2 837 



132 



127 



54 



252 





272 



Ti0 2 .__. 



28 



4 



5 









19 



P 2 5 ... 



13 











13 







S0 3 ---- 



9 







9 











A1 3 3 -- 



110 





20 



27 



63 









Fe 2 3 .. 



21 



1 



2 









18 



FeO 



26 



4 



3 









19 



CaO_._. 



107 



64 









43 







UgC- ... 



177 



68 



109 













KoO_.._ 



104 





23 



14 



63 





4 



Na 2 0... 



22 







22 













1454 , 



273 



289 

 19-87$ 



126 

 8-66$ 



378 

 26-1$ 



56 





Neglecting the small amounts of substances shown by 

 analysis and not introduced into the above calculation, this 

 rock consists of 



Free silica _ 18 



Leucite 26 



Noselite ._ 8 



Diopside 18 



Phlogopite 19 



Accessories „■_ 7 



53-5 



100-0 



The residual amounts form a little magnetite, and there is 

 some titanic acid which may belong to silico-titanates or be 

 present as rutile. The silica is more than enough to have 

 formed sanidine instead of leucite if the conditions had been 

 favorable. 



It is plain that a rock containing leucite, with diopside and 

 phlogopite of the ascertained composition and in the observed 

 proportions, cannot have so high an amount of silica without 

 containing an excess of the acid radical unless some very acid 

 silicate is present. The only possible explanation of the ascer- 

 tained chemical composition, without assuming free silica, is in 

 supposing that the apparent leucite is a regular mineral, of 

 higher silica contents than leucite, with the ratio of alumina 





