we 
JUNE 15, 1899] 
NEAT LS 
B53 
in the flanking crystallines. Profs. Dupare and Mrazec 
give an excellent account of the protogine ; its micro- 
scopic structure and its chemical composition. It isa 
granite, varying from moderately coarse to slightly por- 
phyritic, the silica percentage occasionally fallmg rather 
below that of an average granite. Enclosures of a more 
basic rock are found in it, which the authors consider, no 
doubt rightly, to be included fragments of more ancient 
material and not segregations. The age of this protogine 
cannot be exactly determined, but in other parts of the 
Alps a porphyritic granite, occasionally very coarse, yet 
bearing some resemblance to it, can be seen cutting the 
truly metamorphic rocks, called by the writer the “upper 
schists,” which apparently are the newest among the 
Alpine crystallines. The protogine is flanked on each 
side by a zone of mica schists and fine-grained gneisses, 
which accordingly must be older than it, and it includes 
occasional strips of schist. Of these, some may represent 
wedged-in fragments of the last-named zones, while 
others probably are dykes, modified by pressure. The 
affected by subsequent pressure. These are certainly 
later than the Carboniferous beds, and earlier than the 
lowest Lias, for they occur as pebbles in a conglom- 
erate of that age. lence these “porphyries,” like 
similar outbursts in other parts of the Alps, probably re- 
present Permian eruptions. The authors think them 
not impossibly connected with the vein granites, which 
would assign the latter also to about the same period. 
In discussing the “tectonics,” the authors give an 
excellent 7éswmé of the facts, so far as the immediate 
district of Mont Blanc is concerned, pointing out that the 
fan structure, of which this mass is generally considered 
to be a type, is not by any means so simple or so well 
developed as is generally supposed. They consider the 
central part of the chain to be a vast synclinal with minor 
secondary flexures between primitive anticlinals to the 
north and the south. According to one of them, a section 
across the range exhibits no less than eight anticlinal 
bands with intervening synclinals. On this view, we cannot 
venture to express a definite opinion ; we think, however 
Fic. 2.—Contact of protoxine with crystalline schists below the Aiguille du Midi, seen from the Montagne 
de la Cote. 
whole #zassif is traversed, in some places thickly, with 
veins of a fine-grained granite, poor in mica (aplite). 
The sedimentary rocks associated with the Mont Blanc 
massif belong to two distinct eras. One group occurs 
but locally ; the other has a wide extension, and perhaps 
was deposited over the whole breadth of this region of the 
Alps from north to south. The former group belongs to 
the Carboniferous period. It consists of conglomerates, 
often coarse, grits, and dark muds (now slates) ; the 
latter group forms part of the great Alpine Mesozoic 
series. At the base, Trias is found ; this, however, near 
the Mont Blanc masséf, is either feebly represented or 
absent. It is probably followed everywhere by beds of 
Rheetic age, but these often cannot be separated from 
the Lias. In parts of the Alps the series passes gradu- 
ally upwards into the Eocene ; in this district, however, 
nothing later than some portion of the Jurassic system 
is preserved. Here and there masses of “ porphyry” 
occur (one with, some without, free quartz), often much | 
NO. 1546, VOL. 60] 
‘The schists are at the base of the Aiguille, and of a very dark colour. 
that at present a suspense of judgment would be prudent. 
But that the structure is far less simple than it was 
formerly represented to be can hardly be doubted. 
That great complications exist is not surprising, for the 
region, like the rest of the Alps, has been repeatedly 
folded. The authors recognise the following as the 
principal movements : (1) The Caledonian folding, during 
which the injection of the protogine occurred. This, 
we presume, so far as it can be dated, would be 
earlier Palzeozoic, perhaps post-Ordovician. Then came 
the Hercynian folding, which is supposed to have oc- 
curred in early Permian times, and to be connected with 
the ejection of the “ porphyries.” The axis of this folding 
ran slightly north of east. During the Mesozoic times, 
a subsidence continued, the mountains gradually dis- 
appearing, while deposition went on steadily. 
Then came the Tertiary movements, by which the 
present chain was formed. We cannot attempt to dis- 
cuss this part of the subject, for it is a complicated one 
