Walker - 1967 - A geography of Italy

i*^ '••*t ' ' í S
I
PART I I I : REGION A L GEOGRAPHY
the Engadine over the Stelvio and Resia passes respeaively, the second for traffic
heading for the Brenner from the upper Drau and the upper Piave. Similarly the
Val di Sole presents little difficulty along the most direct route from Milan to
Bolzano, but from the latter northwards to the Brenner the building o f the road
and railway through the Isarco gorge was difficult and expensive. The crystalline
rocks exposed in this zone underlie both the quartz-porphyry plateau and the
high calcareous zone; they are exposed again in the Cima d’Asta range where
they are also associated with granitic intrusions.
The quartz-porphyry plateau, Permian in age and submarine in origin, has its
share of rugged and rock-strewn slopes but it is considerably lower than the
crystalline zone identified above. The immense thickness o f the fiow is revealed
as one ascends the Avisio valley or the gorge o f the Ega river into the heart of the
Dolomites. The exposure o f the red porphyry on one side of the Rolle Pass
opposite the white dolomite on the other presents a striking scenic and morphological
contrast.
For much o f its extent the high calcareous zone rests on the porphyry plateau
and it varies in age from Permian to Cretaceous. The sequence varies laterally but
in general the Permian and lower Triassic rocks consist o f marls, clays, sandstones
and soft limestones; they are succeeded by more clays and sandstones
interbedded with compact limestones and dolomite. The middle Triassic is
represented by a variety o f marine sediments but especially by the resistant
unstratified reef dolomite known as the dolomía ladinica. Higher still comes the
principal or Noric dolomite, upper Triassic in age, very permeable, extensively
fractured and massively stratified. Here and there the Triassic series is capped by
remnants o f Jurassic and Cretaceous limestone, giving an indication o f the extent
o f the demolition to which the area has been subjected.
T he general pattern o f relief and the characteristic morphology o f the Dolomites
have their origin in the near-horizontal arrangement o f the Triassic beds
and in their lithological diversity. There are two fundamental elements : the first
is an immensely thick platform composed mainly o f marls, favouring gentle
rounded forms, but interrupted at intervals by more resistant strata to produce
steeper slopes and broad undulating terraces. This platform which provides many
perfect ski slopes, is deeply incised by valleys, wider or narrower according to
the nature o f the horizon involved, and littered with the debris o f glaciation. To
reach these valleys the traveller may have to follow the narrower, steeper-sided
courses o f rivers cutting through the porphyry plateau, but the climb to the
platform, brilliantly green with hayfields and pinewoods and dotted with farmsteads,
usually offers little difficulty. Once on the platform a widening panorama
unfolds in which the second element in the landscape is revealed; it consists of a
number o f distinct massifs rising above the gentler pasture-covered slopes of
marl or drift and the steeper wooded scars o f limestone to a crown o f gleaming,
waterless dolomite. Where the bedding is compact and massive the summit may
be tabular in form, its rugged surface chaotically sculpted by glaciers and
ic8