134 



W. Cross — Igneous Boohs in Wyoming. 



The CaO is almost exactly what is required for P 2 5 in apa- 

 tite, hence the soluble magnesian silicate must be phlogopite. 

 But if the requisite amount of alumina be taken to form 

 phlogopite on the basis of the magnesia, there remains but a trace 

 of alumina to combine with the residue of the alkalis in leu- 

 cite or any other mineral ; and even if leucite should first be 

 calculated out, assuming all the alumina to be in that mineral, 

 there would remain a considerable residue of the alkalis. 

 Silica is here, too, in excess of the requirements to form any 

 known rock-making silicate with the bases in solution. 



While a calculation of the analyses of 'orendite is impossible 

 without knowing the composition of the peculiar amphibole, 

 yet the difficulty of accounting for the alkalis found is even 

 greater than in the wyomingite, because both analyses show 

 less alumina and more alkali than before. The relation of 

 alumina to alkali is much less than 1:1, whereas in all the 

 important alkali-bearing silicates of rocks that ratio holds good. 



A comparison of analysis Yll with the preceding ones shows 

 that the madupite is even more closely related to the type of 

 the Leucite Hills than might be suspected from the similar 

 developments of the pyroxene and mica in the two cases. This 

 similarity alone led Kemp to correctly characterize the Pilot 

 Butte type as "clearly a variant from the group of rocks of the 

 Leucite Hills." In the presence of the rarer elements, Ce 2 3 , 

 Di 2 3 , Cr 2 3 , SrO, BaO, S0 3 , Fl, 01, and in the ratio between 

 potash and soda this magma certainly shows blood relationship 

 — consanguinity — with the magmas of the Leucite Hills. 



Calculation op Analysis VII. 



Molec. ratio. 



Perofskite 



and 



Apatite. 



Diopside. Phlogopite. Noselite. I Leucite. [Residue. 



Si0 2 711 





346 



120 



42 



203 







Ti0 2 ____ 



21 



21 















A1 2 3 -.. 



90 







17 



21 



52 







Fe 2 3 .-. 32 





2 



2 







28 



FeO 17 





10 



2 







5 



CaO .... 



221 



58 



]63 













MgO.__. 



272 





173 



99 











K 2 0_... 



85 







20 



14 



51 







Xa 2 0_._ 



14 









14 







P 2 5 ... 



11 



11 















S0 3 .... 



7 









7 









Fl 



25 







25 









1506 



90 



694 



285 



98 



306 



33 



From the character of the minerals developed in the madu- 

 pite and the knowledge of their composition obtained through 

 the analyses of the diopside and phlogopite, one may calculate 



