ABSAROKITE-SHOSHONITE-BANAKITE SERIES. 937 
groundmass that is usually dark greenish gray, with a semi- 
waxy luster; but which is sometimes glassy, or phanerocrystal- 
line. The varieties range from those rich in olivine and augite,. 
which with decreasing labradorite grade into rocks of the first 
class, to varieties poor in olivine and augite. Chemically they 
range from 50 to 56 per cent. of silica. Alumina is moderate 
toy high, from 17 to 10.7 per cent. Wime land magnesia are 
moderate to low, the former from 8 to 4.3 per cent., the latter 
from 4.4 to 2.5 per cent. Alkalies are moderately high with 
potash comparatively high for rocks of this region with like 
amounts of silica; potash from 3.4 to 4.4 per cent.; soda from 
BRLOMS On pek Cente molecular ratiolomallkealicsitorsincanisel@ 
and .11. After the crystallization of phenocrysts of labradorite, 
olivine and augite, the remainder of the magma was rich in 
alkali-feldspathic material, which shows itself in the ground- 
mass according to the circumstances of solidification. 
Rocks corresponding chemically to both of these classes 
occur without megascopic phenocrysts, and in various phases of 
crystallization, consequently they differ from them not only in 
microstructure but in the minerals developed. They occur as 
lava flows and as dikes, but no special characteristics can be 
connected with either mode of occurrence, except that the more 
highly crystallized forms are found as dikes. Not all the dikes, 
however, are more crystalline than all the lava flows. 
Rocks of the third class have been found mostly in dikes. 
These rocks are highly feldspathic, with smaller amount of fer- 
romagesian minerals, chiefly biotite with subordinate augite. 
The phenocrysts are labradorite in a groundmass of alkali-feld- 
spars. Chemically they have from 51 to 61 per cent. of silica; 
Gl 7.LO 1.0) alumina; 315) tO) Oypericentlomume .slNtor4ypenicent= 
of magnesia; 3.8 to 4.5 per cent. of soda, and 4.4 to 5.7 per cent. 
of potash. The ratio of alkalies to silica is .13 and.14. Since 
much of the lime and soda go into the phenocrysts of labra- 
dorite, the feldspathic groundmass is rich in potash, and is 
largely orthoclase. The rocks stand at the end of the series, 
where labradorite becomes the prevailing phenocryst, and 
