Editorial Comme?it. 1 1 5 
tation theory of "kerns" of Rosenbusch against which Iddings 
himseh' brings the strongest arguments. 
Brogger's work began in 1890 and has been but lately con- 
cluded. He believes the principle of Soret explains the con- 
centration of the basic silicates on the borders of laccolytes, 
and, consequently the order of appearance of intrusive 
magmas— first the basic and then the more and more acid. 
In that he agrees with Teall. In order to obtain an approxi- 
mation to the nature of the fundamental magma Brogger took 
the average of all the intrusive rocks of the region of Chris- 
tiania, but, according to the author, the extreme richness in 
soda of all the rocks having the "air of family" of the region of 
Christiania, precludes the possibility of accepting Brdgger's 
result as an indication of the nature of the fundamental 
magma, 
Lang (1891) classed the magmas of eruptive rocks into 
four grand divisions according to the relative total quantities 
of lime, soda and potash which they contain, viz: 
1. Rocks in which potash predominates over the sum 
of soda and lime. 
2. Rocks in which soda predominates over potash and 
hme. 
3. Rocks in which the alkalies predominate over lime. 
4. Rocks in which lin^e predominates over the alkalies. 
The author remarks that in such a classification, lime acts 
a double role, from a mineralogical point of view — that is, 
whether it is associated with the ferromagnesian minerals or 
with the silicates of the alkalies ; and further, Lang took no ac- 
count of magnesia which as it appears plays a capital role in 
the natural grouping of magmas. 
The four classes of Lang, based on the relative prevalence 
of the alkaline elements, are in a measure comparable with the 
five principal kerns of Rosenbusch, but in details of applica- 
tion they vary widely. 
Becker has considered six primitive magmas differing 
from each other by their relative contents of calcium, sodium 
and potassium, and has devised an elegant geometric method 
of representing them graphically, according to their analysis 
en bloc. This method is comparable with that of crystallog- 
raphy, in which co-ordinates, h k 1, are variable units, and are 
