PETROLOGY. 151 
leucite in the mode rises, the persalic rocks being very largely or wholly feld- 
spathic, while the salfemanes are almost entirely leucitic and non-feldspathic. 
In the systematic quantitative classification this is well brought out by the fact 
that the majority of the occurrences of sodipotassic subrangs fall in the persalane 
class, as phlegrose (I. 5. i. 3), which is quite common, pulaskose (I. 5. 2. 3), pro- 
cenose (I. 6. 2. 3), beemerose (I. 6. i. 3), and appianose (I. 7. i. 3); while in the 
dosalane class the only sodipotassic subrangs are harzose (II. 4. 3), monzonose 
(II. 5. 2. 3), and shoshonose (II. 5. 3. 3), which are decidedly sporadic, and that, 
finally, no sodipotassic subrangs of the salfemane class are known. 
While the alkalis dominate salic lime as a rule, they do so to a much greater 
extent as the salic components increase, as is shown in the classification by the 
frequent occurrence of peralkalic rangs in the rocks of the persalane class, alkali- 
calcic rangs being observed only in the dosalane class, though they do not occur 
in the more lenic orders of dosalane nor in the salfemanes, the relative increase in 
alkalis, especially potash, and the decrease in alumina here coming into play. 
It has been said above that magnesia dominates ferrous oxide in the majority 
of cases, and while this is true it is especially so of the more femic rocks, notably 
the salfemanes, where the ratio of MgO to FeO is apt to be high. This decreases 
in the dosalanes, and in the persalanes is often about unity, magnesia thus increasing 
relatively to ferrous oxide as the femic components increase or as silica decreases. 
A similar relation holds good of the predominance of magnesia and ferrous oxide 
over femic lime; this ratio increasing on the whole with increase in the femic 
minerals and lenads. 
As regards the minor constituents, both titanium and phosphorus increase on 
the whole toward the femic end, though there are some exceptions. Zirconia seems 
to be most apt to be present in the more salic rocks, especially when these are sodi- 
potassic, and the prevalence of this constituent in sodic magmas is well known. 
Barium shows less regular relations, but it may be said that in general it is some- 
what more abundant in the more femic magmas and especially in those which have 
potash high relatively to soda. Concerning strontium the data are unfortunately 
rather few, and while there seems to be no very general rule in regard to it, there 
are indications that it is more apt to be present in considerable amount in the more 
femic magmas and especially in those rich in lime. But the figures reported for 
it are uniformly so small that they are not conclusive. Chlorine and sulphuric 
anhydride are most common in the sodipotassic magmas, especially when persalic. 
Normative Characters. 
In the annexed table are given the norms of the various rocks, calculated from 
the analyses in the preceding table, and arranged in the same order. A study of 
these norms will give further insight into the chemical relations of the rocks 
and their magmas, especially their relations to the quantitative system, and will 
serve as an introduction to the discussion of their modes or the minerals actually 
present in them. 
