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TTTE rTlAl!A("ri:r.ISTTr'S of TIIK CAUCASUS 37
mound appears incredible. Jii the mountain structure we recognise
a series of primary parallel ridges and furrows, enormously modi-
fied, possibly by subsequent exertions of forces similar to that
which raised the chain,
various forms, but still
certainly
roughly
by subaerial
recognisable.
denudation
How are
in
we
its
to
account for the great clefts that split the crystalline rocks of the
central chain to their base in the U])per Cherek, the Darial and
Alagu- gorges ? We seem to require
the exertion of some strain
acting at right angles to the pi'cssure which raised the chain. The
shi'inkao-e of the Earth's crust, to which the elevation of mountain
regions is now generally attributed by geologists, might naturally
cause such a strain. An alternative theory — held by too high
authorities for me to venture to discard it— is that these gorges
have been sawn asunder by water following its old channels
through a slowly rising ridge of later elevation.
In either case internal forces have produced the rough-hewn
blocks. But other agencies have been at work to model the noble
forms we see around us :
centui-y after century, split
heat
and cold, rain and torrent have,
the mountain crests and furrowed
their flanks. Tee moving backwards and forwards along the
hollows has polished and smoothed their sides, leaving
behind it
as it retired immense loads of the broken stuff' it had carried
down from the higher ranges. Water has followed, scouring the
mountain slopes, tapping the hollows, or filling them up with
alluvial mattei-.^ These agents have done an enormous work,
but they have been sculptors and polishers and cairiers, not
quarriers, and their share of work, even as sculptors, has been
perhaps exaggerated. Like Michael Angelo in his colossal statue
of David, they have had to follow the form of their matei'ial.
' The conservative action of ice could hardly be better sliown than by the contrast between
the upper sources of the Ingur and the Skenis Skali, whicli are closely adjacent. The former
occupy shallow U-shaped troughs, the latter trenches 1000 to 2000 deeper, and V-shaped.
The reason is obvious, at least to those who accept an axiom of Professor lieim which 1 have
elsewhere (Proceedings of the Royal Geographical Society, New Series, vol. x. 1888) pressed on the
attention of geologists. 'Glaciation,' Heini lays down, 'Ls equivalent to the relative cessation
of valley formation.' At the Iiigur sources the glaciers, owing to the configuration of the chain,
always more extensive than those of the Skenis Skali, must have for centuries protected the
slopes from the atmospheric action to which the hills of the Skenis Skali were exposed.