Editorial Co?nment. 1 1 3 
Stripped of all their unessentials it appears that the two 
classifications of the Mississipian series, if they may be called 
two, are to all intents and purposes the same, so far as their 
practical workings are concerned. The fact that the terms 
proposed by professor Williams are not used is not on account 
of any lack of appreciation of his \vork. It is because the 
names are clearly preoccupied to begin with, and because of 
the difficulties already mentioned. In this and all similar cases 
it is the duty of the active workers to try to get together and 
not to attempt to unnecessarily widen unimportant differences, 
which can readily be harmonized. 
EDITORIAL COMMENT. 
The question of the differentiation of Magmas. 
Of the recent publications relating to the origin of the 
variations of the igneous rocks of the earth, those of Rosen- 
busch, Brogger and Iddings being among the earliest, the 
recent brochure of Michel Levy* is one of the most trenchant. 
The author gives a short review of the work of the last ten 
years as expressed in the articles published by Teall, Rosen- 
busch, Brogger, Lang, Iddings, Becker. 
Teall, adopting and applying the principle of Soret of a 
solution of basic silicates in silicates more acid, explained the 
more basic borders of certain laccolytes by the concentration 
of the former class of silicates in the cooler portions of the 
molten mass, hence on the borders of the laccolyte. But, 
(as remarked by the author), unfortunately Fouque had al- 
ready shown (1879) facts diametrically opposite in the dikes 
of Santorin, where the borders are more acid than the centre. 
Rosenbusch's idea of "kerns" or segmentations of the 
primordial 'magma (1889), is only a further application of 
Teall's hypothesis, supposed to take place at greater depths. 
Of these separations, Rosenbusch recognized six primitive 
*Classification des magmas des roches eruptives. Par. A. Michel- 
Levy. (Extrait du Bulletin Soc. Geol. de France. 3 me. ser. XXV.. 
,326, 1897). 
