XIII. GEOLOGY OF THE ALPS. XXXVII
In the heart of Switzerland, and on the extreme northern margin of the
central zone, rises the Central Mass of the Finsteraarhorn from the Lotschen-
thal to the Tbdi. In the centre of this range, where it is intersected by
the routes of the Grimsel and the St. Gotthard, the Granite attains its
most important development, and at the same time the Anticlinal
Axis, or contorted ('fan-shaped') structure of the gneiss is most strongly
marked. Here too, on the N. side, the most striking irregularity is observed
in the contact of the gneiss and its associated quartz-rock with the ad¬
joining Jura-limestone. In the diagonal line from Lauterbrunnen and
Grindelwald to Viesch the fan-shape is fully developed; on the N. side the
strata decline towards the S., in the Viescherhbrner they are vertical, while
on the route from the Eggischhorn (p. 141) to Viesch they assume a N. di¬
rection ; the same is the case in a section of the Grimsel (p. 136). At the
extremities of the gneiss, on the other hand, a uniform and abrupt descent
towards the S. has been observed.
The contact of the crystalline and sedimentary formations is most
strikingly seen on the N. margin of this group, in the profound valleys
and fissures riven through the entire mass by mighty convulsions. The
Gasternthal (p. 251) is a locality adapted for a nearer examination of these
phenomena. The limestone and slate-strata of the precipices of the Altels
and Doldenhorn (p. 147) are extremely contorted in their position; the base
The summit of the Jungfrau (p. 116) consists of gneiss-granite, into
which two masses of Jura-limestone have inserted themselves horizontally,
their extremities being, as it were, folded back. This pseudo-interstrati-
fication must have taken place while the disrupting granite was in a liquid
state. The Eiger and Monch (p. 117), the Mettenberg (p. 119), the Wetterhorn
(p. 123), and particularly the upper part of the Urbachlhal (p. 133) and
the narrow ridge between the Tossenhorn and Gstellihorn display the same
phenomena. Even the extremities of these inserted masses of limestone
contain organic remains of the Jura-formation. This affords a clue to the
structure of the Alps, but if it be considered as evidence that the epoch
of these convulsions is more recent than the Jura chalk and eocene periods,
the soundness of the proposition may be questioned.
The St. Gotthard almost adjoins this central mass of the Finsteraarhorn.
Of a layer of slate and limestone which once intervened between them,
isolated fragments or 'nests' of marble are now the only remnants. At the
level of the St. Gotthard Lakes, granite occurs in the heart of this mass,
at the Gemsboden gneiss, above Hospenthal mica-slate. At Andermatt the
inclination is towards the S., at Airolo towards the N., the fanlike struc¬
ture being here distinctly exhibited , and extending towards the E. as far
as the granite can be traced.
On the Lukmanier (p. 311) these phenomena are repeated; the S.
part of the fan widens as it extends towards the E. The surface, the situa¬
tion of the watershed, and the summit hear no relation to the axis of the
fan; the present configuration of the mountain-chains and valleys cannot
therefore have been occasioned by the upheaval of the granite.
The St. Gotthard possesses beautiful minerals in abundance. Those
in the external central masses display great uniformity, the same species
occurring at Oisans, on Mont Blanc, on the Finsteraarhorn, and on the
St. Gotthard: such are the micaceous iron-ore, titanite , sphene , fluor-spar,
apatite, axiniie, tourmaline, and the whole of the zeolites.
On the S. frontier of the Valais, from the Great St. Bernard over the
lofty summits of the Dent de Rang, Dent Blanche, and the Matterhorn, as
far as the Weisshorn and Simplon, extends a range of crystalline felspar-
rock, which may be regarded not merely as a central mass entitled to rank
with others, but rather as the true Central Chain of the Swiss and Italian
High Alps. Mont Blanc and Monte Rosa, the highest of the Alps, though
not within this mass, are immediately adjacent.
It forms a transition from the fan-shaped mountains , situated nearer
the external (N.) zone of the Alps, to the more horizontally disposed gneiss
which forms the inner crust of the Alps. The fan shape is indistinct;
the symmetrical arrangement of the different rocks is wanting; interstra-
tifications of marble and limestone are more frequent; and serpentine and