198 The American Geologist. September, 1901. 
mon chain. For instance (p. 117), there are isolated lentilles 
of pegmatyte in the schists, these being from one to twelve 
centimeters in (hameter, and similar lentilles arc developed in 
the gneiss, and these are sometimes generated at considerable 
distances from any known granitic mass. 
All these minute, as well as the grander alterations in the 
schists of Mont Blanc, the authors ascribe to two agents 
which acted in conjunction, viz: dynamometamorphism and 
magmatic injection. The work is, in its general conclusions, 
an able contribution to the idea of endomorphism of intrusive 
rocks by the reaction of the intruded rock on the intrusive. 
Frequently the authors find a bordering band of gneiss or 
gneissic schist round about the central massif. This rock is 
sometimes classed as a more perfect metamorphic and some- 
times as a gneissic part of the granite (p. 158). In either case 
the explanation is the same, and in all cases in which granitic 
aspects appear in the schists they are supposed to be due to the 
granitizing effect of granitic injection in the near vicinity. In 
other words the interchange of rock material was mutual and 
in opposite directions. The acid element entered the more 
basic schists, and the schists gave of their iron and magnesia 
to the granite. This process is reasonable, and in some degree 
certain, given the conditions precedent, but it assumes that the 
crystallization of the schists had been produced anterior to the 
appearance of the granite, instead of being the accompaniment 
of it. It is based also on an initial presumption which is not 
taken into consideration, but which is more fundamental. The 
chemical difference between the crystalline schists and the 
granite, from which the authors derive their conclusion of the 
different origins of these two rocks, is local and insufffcient for 
their inference. It is probable that the schists, considered cti 
bloc, including the sericitic schists and all the rocks associated 
with them, would give, in case of complete fusion, a magmatic 
rock identical or similar to the granite of Mont Blanc. 
It seems to the writer, therefore, that there are lacking 
certain links in the argument for foreign origin of the granite. 
On the contrary the granite 'seems toi have an autogenetic 
origin, because : 
I. The widespread metamorphism cannot be attributed to 
contact effect. It is more of the nature of regional metamor- 
