FORMATION OF LEUCITE.IN IGNEOUS ROCKS 269 
to examine these fully, owing to the many combinations possible and 
the almost unlimited number of choices in the matter of variables, 
especially when the femic minerals are considered. But fortunately 
the calculation and presentation of a large number of hypothetical 
magmas is not necessary, and the general principles can be readily 
shown by a few typical cases. 
Still adhering to persalanes, we may introduce anorthite and 
examine domalkalic and alkalicalcic magmas, that is, those in which 
the total alkalies are respectively, three times the amount of lime, and 
equal to it, corresponding to the center-points of the second and 
third rangs. The norms of these would contain quartz, orthoclase, 
albite, anorthite, leucite, and nephelite, in all possible combinations 
and amounts, except that albite and leucite would never occur together. 
These are represented on Plate II. 
In Plate II the black lines represent the loci of persalic magmas, 
the green those of dosalic magmas, and the red those of salfemic 
ones. The orthoclase-quartz line OQ, and the feldspar-quartz area 
OQA, have been omitted as irrelevant to the discussion, but it is to be 
remembered that these quaric areas are always to be understood as 
existing, even though unrepresented. Also the lines which express 
the relations of feldspar to lenad (orders) and of potash to soda 
(subrangs) are omitted, as their presence would complicate the dia- 
gram with little compensating advantage. The dotted lines AtL? 
and L'M will be referred to subsequently. The small squares and 
circles represent the positions of actual rocks, and will be referred to 
subsequently. In the pages which follow, letters in italics, as LON 
for instance, indicate homologous points, lines, and areas in general, 
without specification of any particular kind of magma. 
The solid black lines, marked L?, O', etc., are the loci of persalic 
and peralkalic magmas, which have been treated above, and these 
are identical with the corresponding ones on Plate I. The black 
lines made up of long dashes, and marked L?, O?, etc., are the loci 
of persalic and domalkalic magmas; while those composed of short 
dashes, and marked L3, O35, etc., belong to persalic and alkalicalcic 
magmas. 
Comparison of these three systems reveals some interesting rela- 
tionships. The leucite-nephelite lines L*N?, L?N?, etc., and the ortho- 
