n found near Mesemvria. Other Neogene strata occupy a more
limited space. The Quaternary era is represented by the typical loess,
which covers most of the Danubian plain; to its later epochs belong the
alluvial deposits of the riparian districts with remains of the _Ursus_,
_Equus_, &c., found in bone-caverns. Eruptive masses intrude in the Balkans
and Sredna Gora, as well as in the Archean formation of the southern [v.04
p.0774] ranges, presenting granite, syenite, diorite, diabase,
quartz-porphyry, melaphyre, liparite, trachyte, andesite, basalt, &c.

_Minerals._--The mineral wealth of Bulgaria is considerable, although, with
the exception of coal, it remains largely unexploited. The minerals which
are commercially valuable include gold (found in small quantities), silver,
graphite, galena, pyrite, marcasite, chalcosine, sphalerite, chalcopyrite,
bornite, cuprite, hematite, limonite, ochre, chromite, magnetite, azurite,
manganese, malachite, gypsum, &c. The combustibles are anthracitiferous
coal, coal, "brown coal" and lignite. The lignite mines opened by the
government at Pernik in 1891 yielded in 1904 142,000 tons. Coal beds have
been discovered at Trevna and elsewhere. Thermal springs, mostly
sulphureous, exist in forty-three localities along the southern slope of
the Balkans, in Rhodope, and in the districts of Sofia and Kiustendil;
maximum temperature at Zaparevo, near Dupnitza, 180.5 deg. (Fahrenheit), at
Sofia 118.4 deg.. Many of these are frequented now, as in Roman times, owing to
their valuable therapeutic qualities. The mineral springs on the north of
the Balkans are, with one exception (Vrshetz, near Berkovitza), cold.

_Climate._--The severity of the climate of Bulgaria in comparison with that
of other European regions of the same latitude is attributable in part to
the number and extent of its mountain ranges, in part to the general
configuration of the Balkan Peninsula. Extreme heat in summer and cold in
winter, great local contrasts, and rapid transitions of temperature occur
here as in the adjoining countries. The local contrasts are remarkable. In
the districts extending from the Balkans to the Danube, which are exposed
to the bitter north wind, the winter cold is intense, and the river,
notwithstanding the volume and rapidity of its current, is frequently
frozen over; the temperature has been known to fall to 24 deg. below zero.
Owing to the shelter afforded by the Balkans against hot southerly winds,