192 
IDDINGS. 
ferent kinds of rocks he endeavors to prove the existence of 
certain definite, stoichiometrically proportioned molecules, 
which he terms “ kerns.” It is further assumed that these 
“ kerns ” are capable of dissolving any of the constituent 
oxides or metals in rocks to variable extents, which accounts 
for the impurities in the “ kerns.” The idea is also expressed 
that the differentiation of the general magma has produced 
the magmas which have solidified at some depths within the 
earth, while a secondary differentiation of these partial mag¬ 
mas has produced the rocks which have solidified at the 
surface of the earth. This is in accord with his opinion that 
extrusive rocks differ in chemical composition from their 
corresponding deeply seated forms. He has offered no sug¬ 
gestion as to the process by which a chemical differentiation 
could have taken place. 
The idea expressed by Brogger regarding the origin of the 
igneous rocks of the region of Christiania is that, by some 
process not explained, a basin of molten magma came into 
existence and began to cool at its margin. The magma is 
considered to be a solution of silicates, and a diffusion of the 
less soluble silicates toward the cooler margin is thought to 
be the principal cause of its differentiation. He suggests 
that a partial crystallization may set in and lead to the pro¬ 
duction of segregations. A settling of these crystals to the 
bottom of the reservoir and their subsequent fusion would 
account for the final eruption of basic magmas. The dis¬ 
tinctive chemical character of this natural group of rocks is 
pointed out. 
Vogt’s conception of the differentiation of a molten magma, 
even in extremely localized instances, is that it is due to 
molecular diffusion, without the actual separation (or crys¬ 
tallization) of minerals, and that it may be brought about 
by differences of temperature and of pressure, and possibly 
by magnetic attraction in the case of iron molecules. 
Dakyn and Teall express the idea that in the region in¬ 
vestigated by them the differentiation of a general magma 
took place during the process of consolidation, and that it 
