THE ORIGIN OF IGNEOUS ROCKS. 
121 
magmas with the “metal kern,” Ca Al 2 Si 4 , as the amount 
of this “ kern ” increases the magmas become more capable 
of dissolving the non-aluminous “ metal kern,” (Mg, Fe) Si. 
The differentiation of the original magma furnishes the 
magmas which have consolidated into deeply seated rocks— 
that is, granular ones. The further or secondary differen¬ 
tiation of these magmas have furnished the corresponding 
extrusive rocks. 
He remarks that if we should find the deeply seated rocks 
and the connected series of extrusive rocks of one region, a 
comparison of the chemical composition of both would estab¬ 
lish the laws of the differentiation of magmas ; and he adds 
that there can be no doubt as to the geological and genetic 
relationship between certain deeply seated (or granular) 
rocks and their accompanying system of dikes, and that here, 
then, is to be applied the test for the laws of differentiation, 
which in the paper just reviewed have been evolved from the 
chemical constitution of other forms of eruptive rocks. This 
is said to be the reason why the special forms of dike rocks 
which he has called “ ganggesteine ” have not been taken 
into consideration in this first communication on the subject. 
Rosenbusch’s paper has been critically reviewed by Jus¬ 
tus Roth * in an article on the classification and chem¬ 
ical character of eruptive rocks. In it he states that he 
had used the term “ spaltung ” originally to cover what 
are known as facies of rocks, and cites instances in support 
of his statement that molten magmas of the same or similar 
chemical composition may separate into different associa¬ 
tions of minerals. He remarks that he does not find that 
the analyses presented by Rosenbusch substantiate the law 
laid down by him, that the deeply seated rocks are richer in 
bivalent metals and poorer in alkalies and silica than the 
extrusive rocks. 
In reviewing the treatment of the chemical analyses 
* Roth (J.) “ Die Eintheilung und die chemische Beschaffenheit der 
Eruptivgesteine ” Zeitschr. d. D. geol. Gesell. 8°. Berlin, 1891, vol. 43, 
Part I, pp. 1-42. 
19—Bull. Phil. Soc., Wash., Vol. 12. 
