ough which the Danube finds a passage at the Iron
Gates. The other mountain-systems display great complexity of formation;
beginning with the Dinaric Alps and the parallel ranges of Bosnia, they
run, as a rule, from north-west to south-east; the great chain of Rhodope
traverses the centre of the Peninsula, throwing out spurs towards the Black
Sea and the Aegean; farther west are the lofty Shar Dagh and the mountains
of Montenegro and Albania, continued by the Pindus range and the heights of
Acarnania and Aetolia. The principal summits are Olympus (9794 ft.),
overlooking the Gulf of Salonica; Musalla (9631) and Popova Shapka (8855),
both in the Rhodope system; Liubotrn in the Shar Dagh (8989); Elin, in the
Perin Planina (8794); Belmeken in southern Bulgaria (chain of Dospat,
8562); Smolika in the Pindus range (8445); Dormitor in northern Montenegro
(8294); Kaimakchalan in central Macedonia (8255); and Kiona in Aetolia
(8235). Owing to the distribution of the mountain-chains, the principal
rivers flow in an easterly or south-easterly direction; the Danube falls
into the Black Sea, the Maritza, Mesta, Struma (_Strymon_), Vardar and
Salambria into the Aegean. The only considerable rivers flowing into the
Adriatic are the Narenta, Drin and Viossa. The principal lakes are those of
Ochrida, Prespa, Scutari and Iannina. The climate is more severe than that
of the sister peninsulas, and the temperature is liable to sudden changes.
The winter, though short, is often intensely cold, especially in the
Danubian plain and in Thrace, the rigorous climate of which is frequently
alluded to by the Latin poets. Bitter north-easterly winds prevail in the
spring, and snow is not uncommon even in the low-lying districts of Greece.
The autumn weather is generally fine and clear.

[Illustration] _Geology_.--Broadly speaking, the Balkan Peninsula may be
divided into four areas which geologically are distinct. There is a central
region, roughly triangular in shape, with its base resting upon the Aegean
Sea and its apex in Servia. On two sides this area is bordered by belts of
folded beds which form on the west the mountain ranges of the Adriatic and
Ionian coasts, and on the north the chain of the Balkans. Finally, beyond
the Balkans lies the great Rumanian depression, occupied chiefly by
undisturbed Cretaceous and Tertiary strata. The _central region_, although
wedged in between two belts of folding, is not affected by the folds of
either, except