W. Cross — Igneoits Rooks in Wyoming . 135 



very closely the composition of the glassy base. Assuming 

 that the lime remaining after deductions for apatite and perof- 

 skite is a measure of the diopside of the rock, and that the 

 magnesia surplus after the formation of diopside is all con- 

 tained in phlogopite, of the composition found in the analyses 

 already given, there remains, after calculating out apatite, 

 perofskite, diopside, and phlogopite, a residue of silica, 

 alumina, potash, and soda which is almost exactly that neces- 

 sary for leucite and noselite, calculating the latter from the 

 sulphuric acid, as in the case of the Boar's Tusk wyomingite. 



The result of these calculations is to indicate that if this 

 magma had entirely crystallized, it must have had very nearly 

 the following percentage development of the named constitu- 

 ents : 



Diopside 46-1 ) 65 . Q 



Phlogopite ... 18-9 



Leucite ._ 20*3 



Noselite _. 6*5 



Accessories . 8*2 



26' 



100-0 





The amounts of phlogopite calculated from the fluorine con- 

 tents of the rock and from the magnesia after deducting for 

 diopside agree very closely. While I have been unable to 

 detect a single grain of leucite or noselite in my sections, 

 Kernp refers to a few very minute particles of leucite seen by 

 him. In the calculations I have disregarded the amounts of 

 strontia and baryta in the absence of a good basis for assigning 

 them, although it is known that a part of the baryta is in the 

 phlogopite. 



By comparing the analysis of madupite with that of missour- 

 ite, the granular augite-leucite rock recently described by Weed 

 and Pirsson,* reproduced under XI of the table above, a 

 marked similarity may be discovered. Missourite is richer in 

 magnesia and poorer in lime than madupite, and it has 15 per 

 cent of olivine with only 6 of biotite. As is well known, the 

 quantitative relations of olivine, biotite, and leucite are quite 

 variable in very similar rocks, and under slightly different con- 

 ditions the missourite magma might have yielded more mica 

 and less olivine and leucite. Each rock has about 50 per cent 

 of augite or diopside, and while missourite has 37 per cent of 

 olivine, leucite, and biotite, the crystalline madupite would have 

 had 39 per cent of leucite and phlogopite. It is quite possible 

 that the deep-seated granular equivalent of madupite is a near 

 relative of missourite. 



*Missourite, a new leucite rock from the High wood Mountains of Montana. 

 This Journal, (4), vol. ii, 1896, p. 315. 



