the chain
appears to indicate that a ridge existed in that period. The last
phase in the history of the Caucasus was marked by the growth of the
great volcanoes of Elbruz and Kasbek, which stand upon the old rocks
of the central zone, and by the outflow of sheets of lava upon the
sides of the chain. The cones themselves are composed largely of acid
andesites, but many of the lavas are augite andesites and basalts.
There seem to have been two periods of eruption, and as some of the
lavas have flowed over Quaternary gravels, the latest outbursts must
have been of very recent date.

[Illustration]

Near the northern foot of the Caucasus, especially in the
neighbourhood of the hot mineral springs of Pyatigorsk, a group of
hills of igneous rocks rises above the plain. They are laccolites of
trachytic rock, and raised the Tertiary beds above them in the form of
blisters. Subsequent denudation has removed the sedimentary covering
and exposed the igneous core. (P. La.)

BIBLIOGRAPHY.--Of the older works the following are still useful: A.
von Haxthausen, _Transkaukasia_ (2 vols., Leipzig, 1856); A.
Petzholdt, _Der Kaukasus_ (2 vols., Leipzig, 1866-1867); M.G. von
Thielmann, _Travels in the Caucasus_ (Eng. trans., 2 vols., London,
1875); F.C. Grove, _The Frosty Caucasus_ (London, 1875); G. Radde,
_Reisen im mingrelischen Hochgebirge_ (Tiflis, 1866) and _Vier
Vortrage uber den Kaukasus_ (Gotha, 1874); E. Favre, _Recherches
geologiques dans la partie centrale de la chaine du Caucase_ (Geneva,
1875); Batsevich, Simonovich and others, _Mat. dlya geologiy Kavkaza_
(Tiflis, 1873 seq.); O. Schneider, _Naturwissenschaftliche Beitrage
zur Kenntnis der Kaukasuslander_ (Dresden, 1879), and J. Bryce,
_Transcaucasia_ (London, 1878). The more important amongst the more
recent books are D.W. Freshfield, _Exploration of the Caucasus_ (2nd
ed., 1902, 2 vols., London); A.F. Mummery, _My Climbs in the Alps and
Caucasus_ (London, 1895); H. Abich, _Geologische Forschungen in den
kaukasischen Landern_ (3 vols., Vienna, 1878-1887), _Aus kaukasischen
Landern_ (2 vols., Vienna, 1896), and "Vergleichende Grundzuge des
Kaukasus wie der armenischen und nordpersischen Gebirge," in _Mem.
Acad. Sc. St-Petersb._ (ser. 6, _Math. et Phys._, vii. 359-534); R.
von Erckert, _Der Kaukasus und seine Volker_ (Leipzig, 1887); E.
Chantre, _Recherches anthropologiques dans le Caucase_ (4 vols.,