XXXVIII XIII. GEOLOGY OF THE ALPS.
gabbro, and in the S. part syenite occur. This Central Mass is moreover chiefly
remarkable for its intimate connection with the associated slates, the strata
being in some places strangely intermingled, while in others they gradually
blend. Gneiss and grey slate often occur as an inseparable mass, and give
rise to one of the difficult problems in geology. The basis, a kind of protogine,
is termed Arkesine, and seldom protrudes through the snows and glaciers
of the highest mountains. On the Matterhorn and in its vicinity the level
of the Green Slate, which forms the summit of this gigantic mountain , is
observed to vary as much as 3000', the basis being gneiss and mica slate
which are connected with each other without interruption, as Giordano has
shown. Erosion followed by slips can therefore alone account for the form
of this isolated, toothlike peak, which is probably but a scanty remnant of
a once extensive chain.
Towards the S.W. the masses of Mont Blanc and the Aiguilles Rouges
stand in the same relation to these central masses as those of the St. Gott¬
hard and Finsteraarhorn to the N.E. In these again the fan-structure and
the granitic basis are fully developed. But of these masses it is onlv the
N.E. or N. extremities which belong to Switzerland, those namely which
extend into the S.W. part of the canton of Valais as far as Martigny.
In the Alps of Ticino gneiss and mica-schist predominate. The peculiar
character of the central mass almost disappears. The ill-defined chlorite
talcose, and mica-schists no longer intermingle with the rocks of the basis'
but occupy a distinct position on the outer crust. Gneiss predominates in
the valleys and lower slopes, mica-schist in the higher mountain regions
forming, for example, the crest and summits of the Campolongo Pass as
far as the Pizzo Forno.
The structure is here very complicated, the disruption of the rock
being horizontal, and the lamination of the mica-schist nearly vertical,
while the formation of the basis is much contorted and fractured.
In the upper Val Maggia appears a meridional direction of the moun¬
tain strata completely at variance with their general direction in those
parts of the Alps already considered, and with the main direction of the
whole range. This variation is not confined to the little-known mountains
of Ticino, but may be traced as far as the Upper Engadine, and pre¬
vails throughout the whole chain from the upper Val Maggia to the
Maloja, 54 M. in length, and from Chiavenna to Vals, or about 32 M. in
breadth. This direction and the inclination of the strata towards the E.
appear to bear out the conjecture that Piedmont was encircled with a com¬
plete amphitheatre of mountains before the comparatively recent changes
in the earth's crust occasioned the present configuration of the Alps.
The gneiss which particularly characterises Ticino, first occurs in the
W. in the basis of Monte Rosa and the precipices and cliffs of the vallev
of Macttgnaga (p. 262), the grandest basin in the Alps. In the higher regions
it blends with the mica-schist, of which the four principal peaks of Monte
Rosa appear to be exclusively composed. The main-group rests on a
meridional chain, a huge wall of rock which extends from Stalden (p. 266)
above Vispach to lcrea at the S. base of the range, a distance of 50 M
and throughout half this extent is not less than 10,000' in height. This
forms a barrier between the Pennine and Lepontine Alps.
In a similar manner the Adula Range, to the E. of the Alps of
Ticino, although lower, forms the boundary between the Lepontine and
Rhaetian Alps. This broad mass is bleak and desolate, without strongly
defined summits, and is covered with snow and glaciers which rarely de¬
scend from the heights, the declivities being too precipitous, and not fur¬
rowed by valleys. This is the cradle of the Rhine (p. 366). The meri¬
dional valleys are longer and deeper.
Throughout this group, the strata decline towards the N.E. and E
and gneiss constitutes the basis in the Val Blegno. Indications iff a barrier
between the Adula Range and the Alps of Ticino are observed in the
isolated limestone and marble masses contained in the gneiss near Rosso
and Landaienca in the Val Calanca, which form the connecting links
between the black slates of S. Bernardino and those of the Val Blegno
The gneiss mass which extends along the Splugen Route from Schams
to the Roffna (p. 360) and J'errera (p. 360) attains its most complete