Editorial Comment. 195 
enclosing rocks, they are to be attributed perhaps to later dis- 
turbances, at least to disturbances that penetrated to deeper 
levels and involved rocks that are geneticall)' isolated from the 
rocks which they cut. 
(6) The authors enter largely upon the examination of 
the fragmentary inclusions of the schists in the protogine, and 
then upon a description of those extended ridges of gneissic 
schist which maintain their form and direction over remarkable 
spaces, although embraced in the usual facies of the protogine. 
As to the former the authors reach the conclusion that they are 
masses detached from the original schistose terrane and do not 
result frouT basic segregations from the magma of the proto- 
gine. With this conclusion there can be little, if any dif- 
ference of opinion. In regard to the latter, they find that 
these bands exhibit evident insensible transitions to the pro- 
togine, and are very frequent. "These schistose mtercalations 
are much more frequent than has been supposed hitherto, and 
it would be an error to designate the massif of Mt. Blanc a 
compact nucleus of protogine" (p. 61). As they are less re- 
sistant than the protogine they are easily eroded, and give rise 
to cols and depressions. The authors have discerned the im- 
portance of the relations of these extended bands to the pro- 
togine, in the formation of any theory of the genesis of the 
massif of Mt. Blanc itself. In the col du Geant these schistose 
alternations appear with intervening protogine of differing 
types (p. 65). They reach the conclusion that they are local 
intercalations of the schist in the protogine, or true synclinals 
of the overlying schistose mantle, isolated and enveloped in the 
protogine, but apparently sometimes of a rock somewhat later 
than the schists ; but a greater portion of the inclusions are an- 
alogous to the crystalline schists that flank the protogine. They 
cannot, in any case, be attributed to a dynamic crushing of the 
protogine. 
To the writer these great bands of less granitic rock, 
sometimes approaching veritable schist, appear to be remnants 
of the original fragmental terrane, exhibiting all the transitions 
to protogine, and the same modification in litholog}'. that are 
exhibited by the mica schists. They are central instead of mar- 
ginal, with respect to the protogine, a fact which may be at- 
tributed to infolding or to some great irregularity in the dis- 
