Editorial Comment. 193 
that penetrate the schists in an intrusive manner (p. 22) there 
are other places where there is a gradual passage from the 
schists to the protogine (p. 23) through gneissic and more or 
less augen types. This occurs at the "angle" of the Mer de 
Glace, at Aiguille des Grandes Mantels, at the peak des 
Rachasses, in the summits that overlook the glacier d'Ar- 
gentieres and des Rognous. It is the same on the opposite 
side of the glacier d'Argentiere and in the valley of the 
Durnand ; also at the stairway from Six des Oi"ques to la 
Gurra and in reascending under the stmimit of Grande Becca, 
and elsewhere. Here the protogine passes insensibly into 
gneissic varieties. In the same gorge of Durnand "are seen 
first schistose bands, which little by little become more gneissic 
and which pass evidently to protogine." 
These field appearances are identical with those which 
the writer has described in the final report of the Minnesota 
geological survey and which, prior to careful petrographic ex- 
amination, seemed to him conclusive to prove the cotempo- 
raneit}? of origin of all rocks concerned, and also the origin- 
ation of all the igneous characters of the granite and of the 
gneiss from intense metamorphism and even fusion of the ele- 
ments of the mica schist. The gradual transitions occur, un- 
der this hypothesis, where the original strata were not com- 
pletely fused and displaced or were of differing composition, 
and the abruptly intrusive contacts where the plastic or molten 
matter accompanied and aided by hot water, was carried 
amongst the still infused rocks of the original terrane of the 
region. Where this transference was more gradual, and was 
largely due to water solutions, the pegmatitic structures were 
formed. 
There is an essential difference, as relates to the schists, 
between these hypotheses. According to the authors the 
schists, as schists, preceded the granite. According to the 
writer they are cotemporary with the granite, and represent 
the lower terms of the same process that gave origin to the 
granite. 
(5) The silica of the protogine is found to vary from 66 
to 76 per cent, which shows a granite relatively acid, dis- 
tinguished by that fact from the granite which forms crystalline 
zones exterior to the massif of Mt. Blanc. These variations 
