IQO The American Geologist. September, loui. 
French and Italian geologists have differed on the question 
of the nature and origin of the rock of the massif of Mont 
Blanc, some regarding it as an integral part of the schists, but 
more gneissic, and some as an eruptive rock independent of the 
schists. The authors, however, share with Michel Levy the 
opinion that it is an igneous rock intrusive into the scliists, but 
they lay special stress on the metamorphism of the schists, de- 
veloped by the granite, and the endomorphism of the granite 
produced by the schists. 
The authors accept two rocks, viz : the granite and the 
schists, as independent, unallied facts. They trace out their 
lines of contact and map their separate areas. They make 
petrographical and chemical examinations of these two end 
terms, all tending to demonstrate and emphasize the contrasts 
that separate them in the field and in the laboratory. Then 
they gather together the points of alliance. They find there 
are four terms in the series instead of two terms and that from 
one extreme to the other there is a gradual passage, thus, (i) 
schist, (2) schistose granite, (3) gneissic granite, (4) granite. 
This gradual succession is found not only once, and twice, but 
in many instances. It is an imjportant point in the genetic 
study of the igneous rocks to find this fact so well established 
bv those able investigators, for it has been sometimes affirmed 
that there is no such transition between the schists and the 
granites, and can be none. Reference may be made to page 23 
where the phenomena about the Mer de Glace and the Grande 
Becca are described. This result is identical with that recently 
reached in the investigation of the Archean crystalline rocks of 
Minnesota. This gradation from schist to granite, which 
reasonably interpreted in Minnesota as an indication of an 
original alliance of the two extremes, through the means, in one 
origin, is differently viewed by Messrs. Duparc and Mrazec, 
and the rocks at the extremes of the series are considered as 
separate in origin and in date. They detail at considerable 
length the structural relations of the granite with the schists 
(mica schists) finding it frequently eruptive into the schists. 
Owing to the stratified condition of the protogine Favre 
considered it a granitoid gneiss older than the niica schists 
which envelop it. Lory like Favre ranked the protogine 
amongst the crystalline rocks but vounger than the mica schists. 
