362 HENRY S. WASHINGTON 
keeping the lower edges of the sheet and of the diagram parallel, it 
could easily be seen if the locus of the rock fell within or without its 
corresponding leucitic area." 
It should be said that, in any such study of the relations of rocks 
to their theoretical areas, the data will be, of course, strictly comparable 
only if the analytical figures are reduced to the same condition, by 
eliminating water and other nonessential ingredients and by recal- 
culating the remainder to too per cent. To render our comparisons 
strictly accurate, this should have been done for all the analyses whose 
loci are shown on Plate II. But this would have involved a very 
considerable amount of work and the expenditure of much time, 
which the study did not seem to warrant, especially as it was found 
that the changes in position thus brought about were for the most 
part so small as to be negligible in the scale of the diagram here given, 
except in the case of some manifestly altered rocks, the greater num- 
ber of which have been omitted. 
On examination of the diagram in this way it was found that, 
making due allowance when necessary for rather large amounts of 
water, carbon dioxide, etc., the loci of all the rocks with normative 
leucite fell inside their respective leucitic areas, with two exceptions, 
Nos. g2 and 177, which fall to the right of the area. But the norms 
of these show the presence of kaliophilite, there being therefore an 
excess of potash, so that their position is quite in accordance with 
our assumptions. Of the rocks without normative leucite the loci 
fall outside of the leucitic areas, with the exception of Nos. 104, 105, 
and 106, orendites and a wyomingite of the Leucite Hills. But 
these also have an excess of alkalies, as shown by the presence of 
potassium metasilicate in the norm, so that, while they should fall 
to the left of the line ON, being free from normative leucite, the large 
amount of potash raises their loci so as to make them fall inside the 
leucitic area. It must also be borne in mind that the rocks free from 
normative leucite include the vast majority of all known rocks, only 
a few of which are plotted in the diagram, and concerning whose 
locus outside the leucitic area there can be no question. We may 
therefore consider the proposition as established, namely, that the 
t A square sheet of thin, transparent celluloid, properly marked, would be better 
than the paper. 
