SOLIDIFICATION OF ALLOYS AND MAGMAS 583 
lar to the metal structure on the left, a steel with an excess cementite, 
and a eutectic pearlite, made up of this cementite and ferrite. 
It is not the purpose of this article to discuss these sections in detail 
by trying to point out their methods of freezing; it is desired solely 
to show that two such classes of material as metals and rocks, widely 
different as they are ordinarily considered to be, in reality display 
the same peculiarities of texture. 
FIG. ro 
APPLICATIONS TO IGNEOUS ROCKS 
In endeavoring to point out the similarities in the solidification of 
certain alloys and magmas, one is limited to simple cases to which 
the theory of solubilities is easily applied. That the same considera- 
tions apply to the igneous rocks is indisputable; for it is not a question 
of drawing an analogy between the alloys and rock-masses. It is, 
rather, the application of broad general principles to specific problems; 
the application of general laws of equilibrium which must cover all 
possible cases of solution, even though as yet we may be unable to 
