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THE CHAEACTERISTICS OF THE CAUCASUS .29
portion is 120 miles long — as long as from !Mont Blanc to tlie
Rheinwaldhorn. From Xaltshik to Kutais it is 100 miles broad ;
in its narrowest part about 80 miles broad. A hundred miles is
about the breadth of the Alps from Grenoble to Turin, Chambery
to Ivi'ea, or Lucei'ne to Arona. Contrary, therefore, to what has
often been stated, the Central Caucasus is slightly, but not very
much, narrower than the Alps.
It is essential to an understanding of the chai-acteristics of the
Caucasus, to an appi'eciation of Caucasian scenery, even to the
planning of Caucasian tours, that some correct idea should be formed
of the geological structure of the chain— at any rate, in its main
features. If the zone covered by mountains is nearly as broad as
in the case of the Alps, the orographical detail is much simpler.
Nowhere in the centi"al chain are there more than thirty miles in
a transverse section between the outstanding snow-peaks. There
ai'e about fifty miles between the Wetterhorn and Monte Rosa, or
the Silvretta and the Adamello.
I accept the theory, which has gained ground of late years,
that mountain ranges indicate lines of weakness in the Earth's
crust, and that their elevation is caused by its contraction. The
Alps would appear to be the result of successive and very com-
plicated Earth movements. The Caucasus, by
its more uniform
structure, may suggest rather a single if prolonged effort, whereby
the central core of gneiss and granite has been raised, and the
successive layers of crystalline schists, slates, limestone, and
cretaceous rocks thrown up against its flanks.
The key to a con-ect understanding of much Caucasian orogi'aphy
may be found in the recognition that the geological axis of the chain
and its water-parting are in many places not identical. The granitic
axis emerges from under the waves of the Black Sea, some distance
west of Sukhum Kale. If a line is drawn along its centre in the
accompanying geological map,
it will be seen to form a series of
gentle curves, and to coincide, in the main, with the watershed as
far as the Mamison Pass. I qualify my statement because, east of
Dongusorun and again
above the Skenis Skali sources and the
western source of the Rion, the dividing ridge is for a short space