48 THE ROMAN COMAGMATIC REGION. 
As regards class, sabatinal beemerose lies toward the dosalanes, but is far from 
being transitional. In order and rang it is quite close to the center points, though 
the amount of lime is somewhat high. In the subrang it approaches the dopotassic 
border, though it can hardly be called transitional. 
Analyses of two other types of beemerose are given in II and III. In both of 
these the mode and texture differ widely from the Italian type. Though they 
resemble each other in being holocrystalline, coarse-grained, and more or less homo- 
metric, they not only belong to different types, but exhibit very distinct modes. Their 
analyses are of interest in this connection, not only as they represent a subrang the 
rocks of which are decidedly rare, but still more because these three form another 
excellent illustration of wide divergence in mode with great similarity in chemical 
composition. Comparison of the analyses of these three rocks and consideration 
of the varying modes will repay some study, but would lead us too far astray. 
Mode. The mode was determined by measuring the leucite megaphenocrysts 
on the surfaces of a large hand specimen and by measuring the microphenocrysts 
and the constituents of the groundmass at two magnifications. It can not be checked 
satisfactorily by calculation from the norm, as two feldspars, orthoclase and albite, 
and the two lenads, leucite and nephelite, are present, and the exact amounts of these 
last can not be measured, owing to the texture. To distribute the silica, therefore, 
we would have four unknown quantities and but three equations. The amount of 
nephelite, and consequently that of orthoclase, as the two were measured together, are 
but rough approximations, but they can not be far from the truth. The calculated 
composition of the feldspar is that indicated by the molecules of potash and soda left 
over after using what were needed for leucite, nephelite, haiiyne, and some acmite. 
The amount of haiiyne, calculated as noselite from the SO 3 , is 1.13, so that in this 
case, as in the preceding, the estimation of this mineral is very satisfactory. The 
exact amount of aegirite-augite can not be calculated, as its composition is unknown, 
though an approximation may be arrived at by making assumptions as to its chemical 
composition. If the acmite present is calculated on the basis of the amount of norma- 
tive hematite, the total pyroxene would be about 10 per cent, which is undoubtedly 
much too high. The amounts of augite and magnetite as given in the mode are 
somewhat too high, owing to overlapping, but are probably not far wrong. 
Vol.%. Sp.gr. Wt.%. 
Soda-orthoclase, Or 3 Ab 2 .. . . 71.0 X 2.6 = 184.6 68.5 
Leucite 14.4 X 2.5 = 36.0 13.4 
Nephelite 4.9 X 2.5 = 12.7 4.7 
Haiiyne i X 2.4 = 2.6 i.o 
;Egirite-augite 6. 2X3. 4= 21.1 7.8 
Magnetite 2.4 X 5.2 = 12.5 4.6 
100.0 269-5 100.0 
Comparing the mode with the norm, it is clear that the chief and only impor- 
tant points of difference are in the modal presence of leucite, this being accom- 
panied by decrease in the amounts of orthoclase and nephelite as compared with 
the norm. The type therefore may be described as leucite-salphyro-beemerose. 
