J20 
IDDINGS. 
position that they are capable of dissolving larger amounts 
of non-aluminous magnesian and iron compounds than the 
two magmas first named. This magma is considered to be 
specially susceptible to differentiation, leading to the pro¬ 
duction of aplite and the lamprophyric dike-rocks. It 
seems remarkable that magnesia and iron should not have 
been considered essential ingredients of the hypothetical 
“ metal kerns ” of this magma, since they are such essential 
ingredients of the rocks from which the magma has been 
deduced. 
Another group of analyses, representing basic diorites, 
gabbros, porphyrites, melaphyres, diabases, andesites, and 
basalts, differs from the previous one by a greater proportion 
of the “ metal kern,” Ca Al 2 Si 4 , and a smaller proportion 
of the “ metal kern,” (Na K) A1 Si 2 , with more Mg and Fe. 
These magmas are called gabbro magmas, and are con¬ 
sidered to be very much mixed. 
The last group of analyses includes those with large 
amounts of Mg, Fe, and Ca, and the hypothetical magma is 
called the peridoiite magma. It is composed of the “ metal 
kerns ” (Na K) A1 $i 2 , Ca Al 2 Si 4 , R Si, and R 2 Si in various 
proportions. 
A small number of analyses remain that do not fit into 
any of the preceding groups. The discussion of these analy¬ 
ses leads Rosenbusch to the conclusion that the aluminum 
in rocks is confined to a feldspathic kern, although one of 
the rocks under discussion is an augitite, with 24 per cent, of 
alumina, the mineralogical characteristic of the rock being 
the almost complete absence of feldspar. By these consider¬ 
ations Rosenbusch has been led to the conclusion that the 
magmas furnishing eruptive rocks arise from the differentia¬ 
tion of a primitive magma, and that by this process the 
foyaite and peridotite magmas contain the “ metal kerns,” 
(Na K) A1 Si 2 and R 2 Si or R Si, in almost perfect purity; 
and, further, that these alloys or compounds are insoluble 
in one another, but that the “ metal kern,” (Na K) A1 Si 2 , 
has the power of dissolving Si and Ca Al 2 Si 4 . Finally, in 
