552 Reviews—Hruptive Rocks of the Kristiania Region. 
The melteigite of the Fen region can, as Brdégger shows, be con- 
sidered as derived from an essexite magma by admixture with 
calcite, with removal of certain percentages of anorthite and iron- 
rich pyroxene, and, further, CO,, the former by gravitational smking 
of crystals ; the more leucocratic types, ijolite and urtite, by further 
sinking of the denser pyroxene. 
The ultimate origin of the great mass of carbonate rocks of the 
Fen region raises a question of great difficulty. The complete 
resemblance, chemically and petrographically to the undoubted 
primary dykes of sévite, lead Brdégger to the conclusion that it must 
be regarded as a primary magmatic rock. Its ultimate source must 
be a sedimentary limestone which has been completely melted at 
great depth. By its purity and comparative poorness in silicates, 
it is sharply distinguished from the variable calcareous sediments of 
Paleozoic age in the Kristiania district. Still less does the 
rauhaugite bear resemblance to these, for dolomites are unknown 
amongst the carbonate rocks of the Kristiania region. Brdégger is 
of the opinion that the carbonate rocks must be derived by melting 
(solution) of an older limestone below the Precambrian granite. 
After its melting. at great depth, and separation from the 
carbonate-enriched stem-magma, the great central mass of 
carbonatite is pictured as forming a lighter layer floating on the 
heavy silicate magma. Its intrusion into the crater-neck of the 
Fen led to its crystallization from above downwards. The solid 
carbonate rock thus formed was penetrated in its outer part by the 
silicate magma, giving rise to the vibetoite and melteigite-ijolite 
intrusions. Pneumatolytic addition of phosphorus, fluorine, 
niobium, and tantalum occurred before consolidation, giving rise 
to apatite, and microlite in the resulting sdvite. On its under side 
intimate mixtures of silicate magma and carbonate magma were 
formed, and gave schlieric intrusions of hollaite and kasenite. 
The melteigite-ijolite magma has produced an_ intensive 
contact-metasomatism in the peripheral Precambrian granite. By 
the action of solutions an important transfer of soda has taken place. 
The quartz of the granite is replaced by albite, and the biotite by 
aegirine, oligoclase is converted to albite, and orthoclase into micro- 
perthite and albite, until, at the immediate border, the rock is com- 
pletely transformed to an alkali felspar-aegirine rock—fenite, or its 
more melanocratic type, tveitasite. All possible gradations from 
unchanged granite to the end product fenite can be traced. 
That a transition from granite to aegirine-syenite by in situ 
differentiation is not involved, seems clear from the fact-that the 
destruction of biotite with new-formed needles of aegirine and 
alkali-hornblende and the development of typical “ Schachbrett 
Albit ”’, so characteristic of secondary felspar, can be traced in thin 
sections of the transition rocks. Moreover, in intermediate stages 
some newly formed quartz appears, showing inclusions of aegirine. 
This quartz, unlike that of the granite, is completely free from 
