272 HENRY S. WASHINGTON 
in the norm, except when they are highly potassic, or unless the 
amount of salic lime exceeds that of the alkalies, when its influence 
will be increasingly felt. 
We may now introduce femic molecules into the magma and see 
what influence they exert upon the presence of leucite. _ In order not 
to complicate the calculations unduly, we shall examine only a few 
simple, but typical, cases. 
Let us first assume that the femic mineral is a standard, non- 
aluminous pyroxene exactly intermediate between diopside and 
hedenbergite—with MgO =FeO, and the formula Ca (Mg, Fe)(SiO,),. 
The molecular weight of this is 232, and its silica percentage is 
51.72, intermediate between that of orthoclase and those of 
nephelite and anorthite. We shall also assume that the magmas 
are centrally dosalic and salfemic—that is, with the amount of salic 
minerals in the norm three times that of the femic, and equal to it 
respectively. In the case of the dosalanes we may also consider the 
two cases in which the magma is either peralkalic or domalkalic. 
The variable factors then will be the relations of feldspar to lenads 
and of potash to soda, as in the previous cases. The lines which 
[imit the leucitic areas in these norms are shown in Plate II, the peral- 
kalic and domalkalic dosalanes respectively by solid and short-dashed 
green lines, and the salfemic magmas by solid red lines. ‘The ortho- 
clase-albite lines (OA) are omitted, as unnecessarily complicating 
the diagram. ‘They may be drawn in, if desired, from the points O 
to A, parallel to the lines O'A?, O7?A?, and O3A3. 
Confining our attention, therefore, to the leucitic areas alone, it is 
evident that these are all identical in shape with those of the persa- 
lanes which are homologous as regards salic lime. ‘The lines L4N4, 
L5NS5, and L°N® are parallel to L'N', L?N?, and L3N3, and similarly 
the lines OW are all parallel to each other. On the other hand, 
the peralkalic L4O4 and L°O® are parallel to the peralkalic L'O}, 
while the domalkalic L5O5 is parallel to the domalkalic L707. 
With increasing amounts of pyroxene, the several leucitic areas 
become smaller, until they would vanish (for peralkalic magmas) in 
the pure assumed pyroxene at the point Py, where SiO, =o.862 on the 
line QN, which is also the intersection point of lines drawn through 
the homologous points L?, L4, and L®, and O', O4, and O°. Fur- 
