Walker - 1967 - A geography of Italy

STRUCTURE
plateau and o f east-central Sardinia where rock-strewn rounded summits fall
away to wide, debris-filled valleys. Under the higher temperature conditions
experienced here the granite weathers to much greater depths than in northern
Europe, producing a coarse sand which is easily transported by the winter
torrents. In Gallura the lower relief is largely composed o f such detritus, in
contrast to the irregularly weathered masses o f ‘sohd’ granite which emerge from
it. The greater erodibihty o f the schists contributes to the guUied slopes o f the
Catena Costiera and to the deeply etched network o f the Flumendosa. Peneplanation
has also played its part in producing the plateau-like outlines o f the
Calabrian and Sardinian horsts; erosion surfaces forming a series o f wide
terraces, once thought to be marine abrasion platforms, are particularly well
exemphfied on the western side o f the Serra. From the point o f view o f human
occupation the most significant aspect o f the crystaUine rocks is their hydrology -
a matter deserving fuller treatment in its regional context.
THE VOLCANIC ZONES. Italy is a classic area for vulcanicity which has provided
us not only with a vocabulary but also with the longest historical records on the
subject. Areas which have been involved in the accident o f vulcanicity bear a
family resemblance but each has its own personality; in Italy differences in the
age, composition and mode o f occurrence of the material concerned, as well as
its response to the forces o f erosion, make for a great variety o f landscape - the
splendid active cones o f Campania and Sicily, the wasted giants o f Lazio with
their flooded craters, the sharp hills o f the Sub-Alpine fringe o f Veneto, the
chaotic reUef o f the Monte Ferru complex, and the tabular masses o f the Campidano
and Lugodoro. From the point o f view o f early settlement the volcanic
areas had much to offer - easily workable soils, often o f exceptional fertility,
defensible sites, structures favourable to a regular supply o f ground water, and
a wide variety o f building stones and minerals.
The earliest evidence o f vulcanicity in Italy, which was associated with the
Hercynian orogenesis, is to be found in the western Alps, south-east Sardinia
and Calabria-Peloritani massifs. The lava flows which produced the porphyries
of Lugano, Valsesia, the Ligurian Alps and the Bolzano plateau are Triassic in
age and some, the last-named for example, were o f submarine origin. But the
great volcanic era in Italy arrived with the Tertiary, that is with the Alpine
upheaval. Basalt flows o f Eocene age, sometimes intercalated with contemporary
sediments, occur over sizeable areas in the Monti Lessini, in the Sub-Alpine
foothills between Thiene and Bassano, and along the eastern flank o f Monte
Baldo. In the nearby Berici hills basaltic explosive material predominates, while
the core o f the Euganei hills is o f trach)rte lava.
The Sardinian block was not immune from the shock o f the Alpine movements
and volcanic activity associated with fracturing continued at intervals into the
Quaternary. On the eastern side o f the Campidano rift trachytic and basaltic
lava welled up in contrast to the more explosive activity on the western side,
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