270 HENRY S. WASHINGTON 
clase-nephelite lines O7N', O?N?, etc., are very close together and 
parallel, this being due to the fact that in nephelite and in anorthite 
the relative number of molecules of silica to those of soda and of lime 
is the same in both(2 : 1),while the molecular weights of soda and of 
lime (62 and 56), and consequently of nephelite and of anorthite 
(284 and 278), are approximately the same. These lines, however, 
shift successively to the left or more siliceous end of the diagram with 
the introduction of the anorthite molecule, since the silica percentage 
of this is slightly higher than that of nephelite, 43.17 and 42.25 
respectively. 
On the other hand, the introduction of the anorthite molecule 
reduces the amount of potash present, so that the lines L?O? and 
L303 are successively lower than the peralkalic line L?O'. They 
are also shifted successively toward the right or less siliceous end, 
owing to the low percentage of silica in anorthite. L?O? and L3O3 
are not parallel to L*O’, since they are continuous with the lines O?7Q 
and O3Q, not shown in the diagram, these perpotassic borders ending 
in the common point Q. It will also be seen that the lines O?A? and 
O3A3 are successively lower and more to the right than O'A’, this . 
following from the considerations mentioned above. 
It will also be of interest to examine the relative sizes of the various 
areas, the quaric areas OQA being also considered, as of possible 
interest, though not pertinent to the present discussion. The size 
relations are shown in the two succeeding tables, the first showing the 
relative sizes referred to the corresponding peralkalic area as unity, 
and the second in percentages of the whole area LON. 
It will be seen that, while the leucitic areas become successively 
smaller with increasing lime, yet that relatively to the feldspathic 
areas, OAN, they remain practically constant; this last relationship 
being due to the very slight shift in the diagram toward the left of 
the lines LN and ON. It will also be seen that, as lime enters, the 
leucitic area decreases, as does the feldspathic area, but that the 
quaric area increases, relatively to the whole amount of possible 
magmas. 
All the above relations will, of course, be the same in direction, 
though differing in amount, if the magma is assumed to be docalcic, 
while if it be percalcic the areas will vanish in the point SiO, = 
